When two people have hooked up with at least one person in common, usually used when the number is a lot more.
Thaddeus: Bro, I finally got to fuck Jocinda last night!
Tyrel: That's not coo Thad. We have too much overlap already!
Thaddeus: Come on man. Eunjeung, Latoya, and Ana...so with Jocinda that's 4. You're just jealous that you couldn't get it up and she never came back.
Tyrel: Fuck you man, what about Puja and Juana? That's 6 hoes dude. That's too much.
Thaddeus: Oh shit, you're right man. Too much fuckin' overlap. We gotta stop.