It means that user will no longer see your posts when he browses the forum, and your PMs to that user will also be blocked. Click on the person's name in any post and there is a link to "Block Member"
It has no effect on you or on anyone else on the forum.
"threatening" someone with it is a pretty silly thing to do - if I think someone is a twit, I just block them - I don't tell them about it.
Looking at your posts, I think I can guess why someone would be upset with you. All of your posts are in the buy/sell forum. That is NOT a place where you should be posting comments. Posting comments about someone else's ad is rude. If you have a question, then PM the seller. If you can't PM because your are new, then become active in the forums before trying to use the buy/sell. That's why the rules on PMs exist - so that a member doesn't just sign-up, swoop into the buy/sell, cause issues and then disappear.
Edited by billybob_jcv - 2/1/14 at 12:40pm