be caught with your pants down
be caught with (one's) pants down
To be taken by surprise; to be caught in a vulnerable (often embarrassing) position or situation. When the boss started firing questions at me, I was caught with my pants down and looked like a fool. I just hadn't considered all of those potential outcomes yet and didn't know what to say. We seriously underestimated our opponents on Saturday and were caught with our pants down.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
be caught with your pants downBRITISH, AMERICAN or
be caught with your trousers downBRITISH
1. If someone is caught with their pants down or is caught with their trousers down, they are discovered in an embarrassing situation or in a situation for which they are not prepared. The media was caught with its pants down after the story was proved to be false. He was shocked by the manager's walkout on Friday — and admits he was caught with his pants down.
2. If someone is caught with their pants down or is caught with their trousers down, they are discovered having sex with someone they should not be having sex with. He may have been caught with his trousers down in a brothel, but the real villains are those who threatened blackmail.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012