My best friend and drinking buddy thought of this while out at a bar with a bunch of friends. They dared him to go try to pick up a certain attractive female who was sitting at the bar. He came up with a routine that is just about the perfect way to pick someone up. Hell, this would work just as well if you're a female, and it wouldn't even matter which gender you're trying it on. Just remember that if everyone in the world starts doing this, it'll lose its novelty, and therefore a lot of its effectiveness, so use it sparingly.
The routine is actually very simple. You find someone that you're attracted to, whether they're alone or not, and you go talk to them. Before you even introduce yourself, though, you tell them, "In about five minutes, I'm going to come back over here and hit on you. If you have a problem with that, you can get up and leave. Hell, if you even move over *one seat* I'll know you're not interested and save us both the trouble. But as long as you stay right where you are, I'll be back in five minutes. Talk to you then." Be as charming as possible when you do this. Show confidence, and leave no doubt that you *will* be back in five minutes. Then, leave and go back to your seat.
I guarantee you she's going to watch you go back to your table, and for the next five minutes, she'll probably make periodic glances in your direction. Whenever you catch her doing this, look right back at her while checking your watch. Point at your watch, then at her, if you have to. This is your time to be cutesy and charming. This may also be your time to take a shot of tequila for confidence if you need it. :) As for her, this is her time to discuss you with her friends, and if you're at all attractive and/or well dressed, and even if you're not, her friends will probably be saying all kinds of good things about you. When the five minutes is up, go back and talk to her (assuming she didn't switch seats...you *do* have to stick to your word on this one). You'll be in like flint.
The best part about this whole routine is that you allow the chance for a graceful exit. If the woman decides to turn you down, she doesn't have to say it to your face, she simply has to move. It's a lot easier on both of you this way. Plus, if she only moves over one seat, it allows you to have a second chance: after a significant amount of time has passed, when you go back to the bar for a drink, you can say, "You know, if you had gotten up and walked out, I'd be pretty hurt. But since you only moved one seat, maybe one more drink would have made the difference." Then buy her a drink. By that point, at least you'll have talked to her once and you'll be more comfortable, not to mention it'll be closer to closing time, and you'll both have had a few more drinks. And persistence *does* pay off.