Lol, that overreaction ! "You beat me in a race when we were small kids so now, 10 years later, I hate you and wish you would die, b*tch". That's not crazy at all.
He gets in her face acting all intimidating and shit, that's when she would of said you have 3 seconds to back up or I will kick you so hard in the crotch your ancestors will feel it.
I was... expecting something better for the second male lead to be honest. He looks like an incredibly childish and annoying, one dimensional moron. I'm sure we'll get some more "reasons" for his actions later, but the story would probably be better served if she told him to back the fuck off and proceeded to ignore him for life.