What Can Happen If a Person Purposely Tries to Stress Out Another Person?
When a Person Engages in Outrageous Conduct For the Purpose of Causing Mental Injury the Victim May Sue For the Tort of Intentional Infliction of Mental Distress.
Understanding the Tort of Intentional Infliction of Mental Distress Including Clarity Regarding Medical Evidence
The tort of intentional infliction of mental distress is a rare type of case, and fortunately so; whereas intentional victimizing another person is a anti-social, cruel, and a lacking of common decency towards others. Unfortunately, when such circumstances do arise, especially when occuring within employment relations, serious suffering is endured by the victim.
The elements required to establish the tort of intentional infliction of mental distress, or as may also be referred to as the tort of intentional infliction of emotional injury, among other names for the same tort regardless of the nomenclature, were very directly stated by the Court of Appeal within the case of Boucher v. Wal-Mart Canada Corp., 2014 ONCA 419, where it was said:
 The tort of intentional infliction of mental suffering has three elements. The plaintiff must prove:
- The defendant’s conduct was flagrant and outrageous;
- The defendant’s conduct was calculated to harm the plaintiff;
- The defendant’s conduct caused the plaintiff to suffer a visible and provable illness.
See Prinzo v. Baycrest Centre for Geriatric Care (2002), 2002 CanLII 45005 (ON CA), 60 O.R. (3d) 474 (C.A.).
 The trial judge instructed the jury several times on the three elements of the tort. Pinnock submits that the trial judge misstated the second element. She told the jury:
In determining whether the conduct was calculated to produce harm, you must be satisfied that Mr. Pinnock either intended to produce the consequences or alternatively, ought to have known that the consequences were substantially certain to occur. Has it been established that Mr. Pinnock intended to cause mental suffering on the part of Ms. Boucher, or engaged in conduct that was substantially certain to cause such suffering? [Emphasis added.]
 The alternative, that Pinnock could be liable if he “ought to have known” the consequences were substantially certain to occur, is wrong, he contends, because it imports an objective test into the tort. I am inclined to agree that the trial judge misstated the second element. The test is purely subjective as Weiler J.A. said in Prinzo, at para. 61:
[F]or the conduct to be calculated to produce harm, either the actor must desire to produce the consequences that follow, or the consequences must be known by the actor to be substantially certain to follow.
See also Piresferreira v. Ayotte, 2010 ONCA 384, 319 D.L.R. (4th) 665, leave to appeal to S.C.C. refused,  S.C.C.A. No. 283, at para. 75.
 The plaintiff cannot establish intentional infliction of mental suffering by showing only that the defendant ought to have known that harm would occur. The defendant must have intended to produce the kind of harm that occurred or have known that it was almost certain to occur: see Piresferreira, at para. 78.
Medical Evidence Absence
Whether medical evidence as proof of a visible and provable illness is necessary remains often confused whereas some courts in the past stated that such is a requirement for proof of a visible and provable illness; however, other courts state that such proof can come from evidence that is other than medical evidence such as a personal summary of the emotional affects endured by the victim. In the 2017 case of Saadati v. Moorhead,  1 S.C.R. 543, the Supreme Court, in reference to all torts, clearly stated that proof only by medical evidence is unnecessary. In addition to Saadati, absence of medical evidence was also addressed within Prinzo v. Baycrest Centre for Geriatric Care, 2002 CanLII 45005. Specifically, Saadati and Prinzo state:
 This Court has, however, never required claimants to show a recognizable psychiatric illness as a precondition to recovery for mental injury. Nor, in my view, would it be desirable for it to do so now. Just as recovery for physical injury is not, as a matter of law, conditioned upon a claimant adducing expert diagnostic evidence in support, recovery for mental injury does not require proof of a recognizable psychiatric illness. This and other mechanisms by which some courts have historically sought to control recovery for mental injury are, in my respectful view, premised upon dubious perceptions of psychiatry and of mental illness in general, which Canadian tort law should repudiate. Further, the elements of the cause of action of negligence, together with the threshold stated by this Court in Mustapha v. Culligan of Canada Ltd., 2008 SCC 27,  2 S.C.R. 114, at para. 9, for proving mental injury, furnish a sufficiently robust array of protections against unworthy claims. I therefore conclude that a finding of legally compensable mental injury need not rest, in whole or in part, on the claimant proving a recognized psychiatric illness. It follows that I would allow the appeal and restore the trial judge’s award.
 Concerning the requirement of a "visible and provable illness" it appears that the absence of a medical expert will not necessarily be fatal. In Rahemtulla, supra, McLachlin J. wrote at para. 56: "Notwithstanding the absence of expert medical evidence, I am satisfied that the plaintiff suffered depression accompanied by symptoms of physical illness as a result of Mr. Flack's [her employer's] accusations."
Vicarious Liability Applicable
Of the cases involving intentional infliction of mental distress, many involve employment relationships where an employee alleges the tort of intentional infliction of mental distress against a colleague or manager as well as vicarious liability against the employer arising from the conduct of the colleague or manager. Indeed, this was the situation within Boucher, Prinzo v. Baycrest Centre for Geriatric Care, 2002 CanLII 45005, and Piresferreira v. Ayotte, 2010 ONCA 384, as leading intentional infliction of mental distress cases.
While it may be argued by some that holding an employer vicariously liable for the improper conduct of an employee that inflicts an intentional tort upon a victim, such as a manager who inflicts intentional mental distress upon an employee, the Supreme Court reviewed the concern for vicarious liability of an employer within the case of Bazley v. Curry, 1999 CanLII 692 (SCC),  2 S.C.R. 534, wherein it was said:
37 Underlying the cases holding employers vicariously liable for the unauthorized acts of employees is the idea that employers may justly be held liable where the act falls within the ambit of the risk that the employer’s enterprise creates or exacerbates. Similarly, the policy purposes underlying the imposition of vicarious liability on employers are served only where the wrong is so connected with the employment that it can be said that the employer has introduced the risk of the wrong (and is thereby fairly and usefully charged with its management and minimization). The question in each case is whether there is a connection or nexus between the employment enterprise and that wrong that justifies imposition of vicarious liability on the employer for the wrong, in terms of fair allocation of the consequences of the risk and/or deterrence.
38 Where the risk is closely associated with the wrong that occurred, it seems just that the entity that engages in the enterprise (and in many cases profits from it) should internalize the full cost of operation, including potential torts. See generally A. O. Sykes, “The Boundaries of Vicarious Liability: An Economic Analysis of the Scope of Employment Rule and Related Legal Doctrines” (1988), 101 Harv. L. Rev. 563. On the other hand, when the wrongful act lacks meaningful connection to the enterprise, liability ceases to flow: Poland v. John Parr and Sons,  1 K.B. 236 (C.A.) (noting that the question is often one of degree). As Prosser and Keeton sum up (Prosser and Keeton on the Law of Torts (5th ed. 1984), at pp. 500-501), when the harm is connected to the employment enterprise:
The losses caused by the torts of employees, which as a practical matter are sure to occur in the conduct of the employer’s enterprise, are placed upon that enterprise itself, as a required cost of doing business. They are placed upon the employer because, having engaged in an enterprise, which will on the basis of all past experience involve harm to others through the torts of employees, and sought to profit by it, it is just that he, rather than the innocent injured plaintiff, should bear them; and because he is better able to absorb them, and to distribute them, through prices, rates or liability insurance, to the public, and so to shift them to society, to the community at large.
Accordingly, per Bazley as shown above, even where an employer is unaware of, and thus without authorization or condonation of, the tortious intentional infliction of mental distress conduct of an employee, the employer may be held vicarious liable.
The tort of intentional infliction of mental distress involves conduct deemed "flagrant and outrageous" that was "calculated to harm" the victim and results in a "visible and provable illness" to the victim.