All talk and no trousers
When someone talks about someone else in a way that would suggest that they had slept with someone, but had in fact not.
Dude 1: I banged her so hard last night!!!
Dude 2: Haha!!! Really?
Dude 3: Man... you're all talk and no trousers
Dude 2: Haha!!! Really?
Dude 3: Man... you're all talk and no trousers
All talk and no trousers
A bloke who talks about having sex, but lacks the balls to do it.
"Dave keeps promising to give me a great sex session, but bottled out of it. He's all talk and no trousers!"