1) Expression of victory or happiness of the result of a given situation.
Get in (there)
2) Phrase used to encourage another to do something dangerous or exciting, usually when they show signs of wanting to do it anyway.
1)
CARL: "Here, Pete! Jenny says she wants to give you a hand-job."
PETE: "Get in! Where is she?"
2)
JENNY: "You like that?"
PETE: "Oh yeah, harder bitch! HARDER!"