It's been said so let me just start by saying it again. Audience Management.
It's vital, and it's what you are missing.
When you have a heckler you need to very quickly decide where on the heckler scale they are, and weather or not alcohol has anything to do with it.
My heckler looks like this.
Heckler-O-Meter
1: The spectator isn't a real threat. Just trying to have some fun by harmlessly interjecting their humor once or twice into your act. Take note of any funny bits they have, and then use it in another show!
5: The spectator is a problem to the act but isn't a hostile threat. Maybe they are out with friends and or family and perhaps just trying to look cool.
10: The spectator is an active problem and should be considered hostile. They are disrupting the show, and intentionally trying to mess you up. They should not be used for any effects.
Naturally alcohol is a problem and can enhance or horribly worsen their behavior. Use your best judgment when booze is involved. You can not reason with a drunk. Don't even attempt it. Have them removed by security.
Usually with a spectator who is between a 2 and a 7 you can try a heckler line like: "That's funny. I read the script and you didn't have any speaking parts." and usually they shut up. For someone whose just a 1 on my scale I rarely if ever bother with them. I laugh, take note of what they said, and move on.
For you're serious problems, you can try a heckler line on them but chances are if they are going to be hostile it probably won't work. It will just entice them to act up more.
People heckle because they want to be the center of attention. They want to be the show. Some people are content with only sharing a brief moment of the spot light with you, while others would rather be the entire show themselves, especially if they think they have more to offer than you do.
When you acknowledge a heckler, or even use a heckler line you invite them into your act. You give them power (and permission) to engage you in conversation. In short, you give them the spot light. So if you get one whose a problem to your act, just ignore him and move on. The minute you break to engage them is the minute you've just given up control.
Audiences hate hecklers who are disruptive just as much as you do. If you just simply shut down and refuse to work the audience usually takes care of their own.
That brings me to my last point. In the absolute worst case senareos, like an 8 or above, you may be wise to just shut down the act and leave stage if necessary until the heckler is dealt with. Also, don't be afraid to call security or the bouncers to have the guy escorted out. Remember, it's YOUR show. You are the one in charge.