Can be used given the right time regardless that you were originally in the conversation. Be warned though, results may vary.
You: Hey (insert name here), I heard that you were murking around that chick's house the other day.
2nd Person: ummmmm yeeeah........
You: Save it for the bedroom.
This Guy: So, you managed to let that guy get it in you.
That Hot Chick: Uuugh! I never let him in! Who the fuck is talking shit about me!
You: Slut, Save it for the bedroom.