If someone makes a real name username and you don't do anything else about it, you should be fine. However, if you take that username, look up the user in the

If someone makes a real name username and you don't do anything else about it, you should be fine. However, if you take that username, look up the user in the real world and send spam without consent you are in deep shit. It's all about consent of use and for what. The user has implicitly given consent to use their username as a username but nothing else.