And there it is, thats 99.9% where you're problem came from. If you roll into some other guys group by yourself and especially when you do center of attention stuff like play guitar and sing, they are automatically going to be hostile to you.

Next time you roll onto someone else's turf (although you said it was one of the girl's place this guy obviously saw it as his back yard), bring at least one friend and leave the guitar at home.

When you look at it logically, while the other guy was obviously being a dick, what he did worked. He got rid of you and kept his girls for himself.