be caught with pants down

be caught with your pants/trousers down

1. to be suddenly discovered doing something that you did not want other people to know about, especially having sex Apparently he was caught with his pants down. His wife came home to find him in bed with the neighbour.
2. to be asked to do or say something that you are not prepared for He asked me where I'd been the previous evening and I was caught with my trousers down.
See wouldn't be caught dead, fall between two stools
See also: caught, down, pant