How to Murder Your Wife(1965)

Stanley Ford is a successful cartoonist and happily single. That is, until he gets drunk at a friend's bachelor party and impulsively proposes to the beautiful woman who pops out of the cake. Once sober, he regrets the decision, but she won't agree to a divorce. Stanley jokingly vents his frustrations in his comic strip by having the main character kill his wife. But when his actual wife goes missing and Stanley is arrested for her murder, he has a change of heart.