Caught with his pants off

Catch someone with his pants down (off)

1.- to make someone feel embarrassed by arriving or doing something when they are not ready.

We spent a lot of time preparing for the inspection; we didn't want to get caught with our pants down.


2. - to discover that someone is doing something that they should not be doing or has not done something that they should have done.

He’s not just the first politician to be caught with his pants down, and he won’t be the last.

No difference.

It means being get caught on the act/spot of the crime.

除了一般的犯罪行為外，今天有時引伸為捉姦在床的意思。

caught with his pants off.解被人發現到沒有穿褲子。
caught with his pants down.解被人發現褲子鬆脫在腳下。

Caught with his pants down (or off)

試想想, 有個賊剛脫了褲大便, 即時比警察拉, 又倒楣, 又尷尬, 脫了褲又不能逃跑.

http://www.answers.com/topic/caught-with-your-pants-down

有時可解作坐屎監