When walking into a very ordinary nightclub to find only one very hot looking woman, 9 times out of 10 she will be acompanied by a very dirty looking woman. In order to hook up with the hotter of the two, one of your mates must distract the dirtier one by hooking up with her.
Hooking up with the dirty one is known as making "the ultimate sacrifice".
Furby and Mick walk into the Pavillion, Sydney.
Mick: Look at that stunner over there!
Furby: She is gorgeous.. but look at that ugly mole she is with
Mick: Furby... one of us has to make the ultimate sacrifice...
Furby: .... I want to make the ultimate sacrifice...