An act ‘for one’s own purposes. It describes circumstances when an employer is not vicariously liable for the tort of his employee because the latter was not acting in the course of employment as he was ‘on a frolic of his own’, i.e. engaged in an activity on his own account. In Hilton v. Thomas Burton (Rhodes) Ltd (1961) demolition workers left work in the employer’s van to go to a cafe. The driver, an employee of the defendants, was negligent and the foreman was killed. The defendants were not liable as the men were on a ‘frolic of their own’.