A frolic of his own

Battistoni v. Thomas, [1932] S.C.R. 144:

On the other hand, if the unauthorized and wrongful act of the servant is not so connected with the authorized act as to be a mode of doing it, but is an independent act, the master is not responsible; for in such a case the servant is not acting in the course of his employment, but has gone outside of it. He can no longer be said to be doing, although in a wrong and unauthorized way, what he was authorized to do; he is doing what he was not authorized to do at all.