catch with one's pants down

catch with one's pants down  {v. phr.},  {slang}
To surprise someone in an embarrassing position or guilty act.
They thought they could succeed in the robbery, but they got caught with their pants down.
When the weather turned hot in May, the drive-in restaurant was caught with its pants down, and ran out of ice cream before noon.
Categories: catch embarrassment {slang} {v. phr.}