Dirty Tricks...

I was hoping we could start a thread on all of the little tricks that people use in the ring; the headbutts, shoulder checks, nut-shots, etc...Cause despite the fact that they're illegal blows (and possibly not the most honorable of approaches), there are techniques involved and they are important to know. So please add to this list any tricks that you know of/use/have had used on you.

Headbutts:

Mal: The hardest part of the head is right around the top of the forehead (I believe that is where the bone is the thickest). Therefore, that is probably the part of the head best suited for bashing someone in the face.
Inside work: On the inside the head doesn't strike me as a very effective weapon (I mean inside, like in a clinch). I've seen guys try and use the side of their head, but that seems like a stupid move as your temple is on the side of your head, and you run the risk of damaging yourself as much as your opponent. (In a clinch you're probably looking for more of a shoulder-hop, but that'll be a different post). The head is effective on the way inside. Look at guys like Joe Frazier who fight in something of a crouch, and who like to work up close. When you're approaching your opponent, going into a clinch or whatever, if your head is lowered you'll end up with your forehead either in his chest or in his face. This is probably the most effective (and discreet) way to pull off a headbutt, because you're not actually reeling back and lunging forward with your head the ref is less likely to call it intentional. However, (and I really think this is important) using your head is really a double-edged sword. The chances of you opening up a gash on yourself are just as good as on your opponent; equally, the blunt force of a head on head collision is likely to effect both fighters in a similar fashion. So, it's kind of a null-move. There's really no guaranteed benefit from it.
Aim: Okay. If you're still insistant on headbutting your opponent: There are obvious "soft-targets" that you'd probably be aiming for. One obvious one is the nose. Just look at where guys are most often cut from headbutts: the cheek-bones, and the soft skin around the eyes. You DO NOT want to collide forhead to forhead. Ha!
Sparring: Well, you'll be wearing a helmet, so that's good. The only thing that could be worked on in sparring (that I can think of) is the "on the way to the inside" approach that I mentioned above. Come in low, head slightly lowered, and bring your head up into your opponent.

EXTRA NOTE: Headbutting (intentionally) in my opinion is stupid. You run the risk, not only of opening up a cut, but possibly injuring your neck/spine depending upon if you do it incorrectly. At the same time, you're still hitting your head against something, which in essence is the same as taking a punch, it's causing the brain to move in the skull, and that's no good. Of all the dirty tricks, headbutts seem to me the least effective.