usually using big words makes the users look stupid more than anything....when you have a debate with someone whether here or in real life chances are the other 5 or so people witnessing it are all going to go "Huh?!? that's not a real word." when you pull out some creative vocabulary.
I have found direct insults work the best when they are called for. You can't fight them any other way if they aren't going to act rational to begin with.