C.U.P.I.D. stands for "Cunt Until Point Is Disproven" and is a system for choosing friends which weeds people out by instantly assuming everyone you meet is a twat until they prove to you that they are not.
B: The cunt! But i thought you two were mates.
A: I know, I know I'm too trusting I should have used the c.u.p.i.d. system like Alex said.
B: Oh well at least you'll know for next time, lets go get pissed