Why do guys usually play nice at first?

...then when they don't GET what they want or HEAR the answers they want they start to let their true selves out and treat the woman like a piece of garbage? And don't say "hang around with better men," b/c I don't hang around them, because they untrustworthy. I'm going off of what I see, they are really quick to turn on a woman and degrade her when it's not going their way. I thought they said they were 'nice guys' LOL. (yea, right).