In the use of the term by a male, 'It' would be the erect male phallacy. i.e. she would 'get it', implies that "she invites my male genitalia''
Tom: Don't be such a pussy! GET IT! GET IT!
"Man, did you see Nick turning Katie's pants blue? He was GETTIN IT.
2.) "Oh no! My bus will be here any minute!" / "Get IT!"
3.) (gritting teeth before exercising with obviously light weights) "Get IT!"
4.) (dog snarling, about to chase its own tail) "Get ITTT!"
A teammate could shout, "Get it!" to you when you're fighting for a ball during a game.
"Oh uh, nice outfit.. get it." - a sarcastic compliment, which really means the speaker believes you look ridiculous and wonders what you were thinking that morning.