When you have plans to pull a girl but invite a good mate who you can chat to if the plan fails.
Man 1: Hey do you wanna go out tonight? I just got invited out by George, he says Samantha and a few of her friends will be there.
Man 2: Doesn't he fancy Samantha?
Man 1: I think so, why?
Man 2: You're so his banter back-up!