The meaning of "caught with your pants down" is:
The definition of "caught with your pants down" is:
(idiom) found in an embarrassing situation
I drank too much at our work party last week. I got caught with my pants down when the boss saw me! I was so embarrassed!
My roommate was caught with his pants down when my girlfriend accidentally saw him naked in the shower.
Mark caught me with my pants down when he came into the bathroom without knocking.