hdtv, have you ever considered that maybe those girls are asking you out as a joke? That's the only explanation I can think of, if you're being so obviously unfriendly. Maybe they just want to see how much they can piss you off.
you can't blame that on him if he's gone through the rough times in his past with bad people in his life. he talked about how other people with bad intentions tried to scam him or rip him off or practically steal from him. so of course he's not gonna be able to trust many people.
those girls may not realize what he has been through and think that he should react normally like everyone else does, and since he doesn't give responses, they might try until they get bored and move on.