trolling

Being a prick on the internet because you can. Typically unleashing one or more cynical or sarcastic remarks on an innocent by-stander, because it's the internet and, hey, you can.

Guy: "I just found the coolest ninja pencil in existence."
Other Guy: "I just found the most retarded thread in existence

http://www.urbandictionary.com/define.php?term=trolling