Anywhere it's frowned upon to use profanity. Years ago I fell into a terrible habit of throwing an obscenity into a sentence instead of a dozen umms leading up to the word I'm going to stutter on. Saying "this f'in pizza is amazing" around my friends during the big game is acceptable. Not so much around grandma. But a certain place I always stutter is at the mechanic's. Trying to explain what's wrong with my car while stuttering and switching around words is brutal.