Why do some guys think I am dumb during a hook up?

They don’t know me well and think things that aren’t true about me one guy called me a retard during our hook up and he think I didn’t understand things when this isn’t true about me at all. I even have text to prove it. Why do guys think it’s ok to treat a girl this way during a hook up when she is not mentally disabled? Why do they think it’s ok to think untrue things about me?