When someone says something to a member of their sexually preferred sex that is so obviously flirting. when this happens, anyone around that person normally shouts out BC.
The announcement of BC can often lead to cock blocking.
Guy: you look amazing (to a girl)
Friend 1: (insert name) is so hot!
Friend 2: I think you should try it on.
Friend 1: I'm going to lay down a cheeky BC.