Vicars are inherently funny. British vicars are generally portrayed as docile and gentle elderly chaps, with white hair and little glasses and ever so prim and prissy ways. They drink take afternoon tea ("more tea, vicar?"), have a tendency to be a bit liberal with the altar wine and don't believe that anything remotely sexual happens ever, despite the fact that Church of England vicars are allowed to marry. So, to be caught in flagrante delicto--or even mistaken for being so--by the vicar is, of course, the second funniest thing ever. Catching the vicar in the act is the only thing funnier.