Imagine you are talking to a hot girl you just met in a bar, club, or concert and having a discussion. Suddenly a random bystander (after overhearing it) injects himself in the conversation and is only speaking to her and only rects when you explicitly talk to him. Of course he is not interested in you, only wants to steal who is with you.

How would you react to this interaction? I mean, if she is speaking to him leaving you be the third wheel it is very hard to say to ask him to leave.