It means a few things typically. It means
1) A person is making stupid posts not related to the forum we are in.
2) It means the person is asking questions along the lines of "What is test e?" or "Can I drink winny?".
3) The person is not using the search option or making an effort to educate themselves, but posting up questions that can be answered in a few minutes if the search option is used.
4) It means they have an attitude or come in here ripping on people/vets/mods trying tohelp them.
5) It means they are looking for sources or discussing prices in the open forum or via PM.
6) They have broken a rule or some sort or are a liar.
7) ETC, ETC, ETC.