Personal attacks. Emmitt got suspended for multiple warnings for making on other posters (calling them stupid or specifically their "brain sucks"
) way way back in the fall of 2007. And he was only suspended for 7 days.
Don't call people names, don't call them stupid. You can call someone ignorant, which is a more aggressive way of saying uninformed, if it's in regards to a specific subject, but not so much when you use the term to sub for the word stupid.
There was much more tension on the board in those days, since then I've cut a lot of slack.
You almost certainly get at least warning. Blatant and repeat offenders may face suspension. Basically if you do enough to get suspended more than once, then there's a chance you could get banned permanently.
But it's never approached that. One guy, JRizzzle who happened to be the first to get suspended got a 30-day suspension for calling people names. Then came back, was civil for a bit, and then resorted to name calling again, and got suspended once more. He hasn't been back since. He wasn't a big fan of people that didn't worship Vick.
I'm sure somebody out there is thinking how much of a [insert female genitalia euphemism] I am for forbidding name calling. But one insult leads to another and then leads to a flame war. And flame wars are the worst. So you nip it in the bud at the start before it spreads.