"I am Offended!"
Other than trolling, I don't think most people "reinvent" themselves. (some, yes...especially very shy people).
Most of us just tend to be less self restrictive. It's human nature to want to cuss, but we know that if kids are around, we will self-censor. We also self censor more when we are eye to eye. Studies show you are far less likely to lie, cheat, or be abusive face-to-face. So the internet is perceived by our subconscious to be a giant dark room with people we do not know or never will who are all grown up adults.