Or never write anything you don’t want broadcast in open court.

 You can be sure that if opposing counsel can make you angry enough to lose your cool, he’ll take advantage of it in a motion which he will most assuredly find occasion to read in open court before the judge and not a few of your peers.

A corollary to the above rule is that civility is not just for losers. Insulting the other party or counsel in a brief or argument only distracts from the merits of the legal argument – unless of course you don’t have any meritorious legal arguments, in which case the lack of civility will only amplify that fact.