If one's TOS was worded right, and the community rules helped back up the TOS, then typically one wouldn't have a problem.
Generally speaking, most people will use the ploy of saying they will contact a lawyer if you do not remove their stuff from your forum, but it almost always is a bluff, just to try to scare the admin into doing what they want to do. Most people do not have the money to hire a lawyer to do such. And as such, if they do manage to do so, one better have a good TOS, and a set of rules to show that the person doing such is in the wrong.
If I were to receive a threat like that, I would request that they get a lawyer, and have them submit a formal legal request, and to have that lawyer get all of the information needed to prove that the user was in the wrong. Though personally, I don't think they would be able to get far enough to do such, especially if the person was under the age of 18.