Why do the British say "have it off" and the Americans say "get it on"

[raccoon]

and it means the same thing? (To engage in sexual intercourse.)

[Lydia Leftcoast]

1. Both are slang, and slang is extremely local

That's all I can tell you.

[petronius]

2. Because Americans are more forward looking, and the British tend toward

retrospectiveness. Hence the difference: one sounds more present/past tense, and the other is more future tense/about to start...

:)

(Yeah, I'm talking out of my ass/arse here...)