People who’d never say something horrible in real life will do it again and again and again online. It’s like the behavior of crowds, or those mass beatings where no one gets blamed because everyone’s at fault.
When someone tries to mess with you, tries to cut you down, tries to tell you that you’re not worth something – LAUGH IT OFF. It is important to remember that. You can always go and take out your aggressions elsewhere, like at a gym. But as far as your public persona is concerned, you MUST be your own PR representative. Don’t let it get to you.