Read When I Say No, I feel Guilty by Manuel J. Smith.
I realize that this book sounds like it has nothing to do with your situation, but before you dismiss it out of hand, I implore you to read some of its customer reviews on Amazon.
Note that it's a book that is best read backwards, from the back of the book, where the examples begin, to the front of the book, where the theory is actually discussed.
On that note, someone else mentioned using sarcasm, but the book and I would advise against that. It's important that you do not throw verbal stones back at him and it's important that you do not scold him and make him lose face in front of his classmates. If or when that student crosses the line, ask to speak to him privately. Once alone with him, assuming you feel safe enough to meet him privately of course, he won't have an audience to play for, so he's much less likely to act out if you can be assertive about what you want from him.
Next, I'd suggest that you take up some kind of combative sport, like martial arts, or boxing, or even a sport like rugby. This is not to encourage you to fight, please do not misrepresent my intent, this is just to teach you how to carry yourself with confidence and to mitigate some of the fear of a physical confrontation.
Next, I'd suggest that you practice public speaking in a safe environment. The best place for that is http://www.toastmasters.org/ (it's a non-profit club, so it's a cheap way to practice public speaking and to bring up some of the problems you've been having in class and discuss possible ways to address them).
Just one warning thought. Not all Toastmasters clubs are equal. If you don't like the vibe in one, try another one, and if you don't like that second one, try a third one. They're basically everywhere and there are many to choose from. The key is to keep on going, and to participate, even if you don't feel comfortable at first. If you go frequently enough, you'll feel comfortable enough and it can become like a second home to you.
Next, and this is the most difficult challenge I can give you, so I don't really expect that you'll do it. But once that you've done all those three things I've suggested, I'd encourage you to take it up a notch higher, and that's to join a comics class sponsored by a night club, or to participate in poetry slams, or even to sing at Karaoke clubs, all the while staying completely sober. I'm not saying any of these things are going to be easy, especially not for the type of personality I envision you to have, but if you can do any of these things (without the help of alcohol), handling a single heckler in your class will seem like a real walk in the park after that.
Please note that these things are worth doing, even if that guy ends up dropping your class. Our society tends to reward confident and extroverted people. And aside from the book I've suggested, which is one in a million, nothing beats practicing frequently and sharpening yourself against the brunt force of a real live audience.