What do you do? Enter the discussion with your opinion and ignore the jerk?
Sometimes. In some real-life, face-to-face conversations, with the more full communication available, the jerk is easier to manage than in plain text.
Stay out of the discussion all together to avoid being related with the jerk?
I may stay out of the discussion, but not for your stated reason. The jerk may just make the conversation unpleasant, and then I may just not engage.
"Join" the other side just to oppose the jerk?
No. That's just making it personal, which is a bad scene.
Are you a good debater in person?
Depends what you mean by "good debater".
There's formal debate, which has a scoring system and which can be won or lost. But most folks aren't actually learned of the forms - they remember that you're supposed to win or lose, and they forget the purpose of the exercise, which is to explore a topic to see what grains of truth can be found.
That forgetfulness means that most modern social situations are not appropriate places to really debate things - the winning and losing hangup becomes a real issue that can louse up a social gathering something fierce.
Places like EN World offer more appropriate settings for debate. However, on the internet these days, there's folks still caught up in the winning and losing. Some feel that refusing to back down, getting the last word, making the other guy lose their cool, playing tricks with semantics, or saying things you can snigger about in private conversations counts as good debate. I'm not one of those people. Debate isn't about scoring points within a social group, or taking people down a notch in ego.
Edit: I'm talking about people in general, folks. Not OTTers in particular. Not everything in the world is about OTTers.