Then politely point out the times he did beforehand. Did he not do enough research and make a politically-charged article in the past? Then that's germane to the conversation. We'd like to hear about it.

But calling somebody a jackass is not.

One amusing incident was when he took Microsoft to task for creating a "System Idle Process" that uses up all his available CPU time. That's about the time I stopped reading his column.

There are many other examples: http://www.google.com/search?q=john+dvorak+idiot or http://www.google.com/search?q=john+dvorak+moron

Someone already pointed out his "screw ups" so I will not repeat them.

Anyone who "screws up" quite a lot I think it is fair to call him a jackass. ie, Arrington

No, it's ok to call them incompetent. However it is ok to call self-admitted trolls jackasses, so you're safe :-P