You and I are debating X. You claim that X is true, while I claim that X is false.
1. You say: X is true because Y.
I say: No, fuckburglar, X is false because Not-Y.
This is not an ad hominem fallacy. It is a valid argument containing an insult. To truly commit to the fallacy, avoid valid arguments.
2. You say: X is true because Y.
I say: No, fuckburglar, X is false because you burgle fucks.
This is the ad hominem fallacy in its proper form. The truth or falsity of claim X has nothing to do with whether or not you actually burgle fucks. A mere insult is lazy; it lacks the fallacious flavor of the juicy ad hom.
I hope this has been helpful. We really must elevate the dialogue, you know?