I had an idea that I have not tried yet: Go up to a girl and say "Hey, can YOU buy ME a drink?" And see what they say... If they laugh, then thats good! If they don't then get away. Think of something original. Do not stay more than 5-10 minutes. What is the first thing someone thinks when you walk up to them? Its "When is this person going to leave?" So you gotta get in, get the digits, get out.
They want something different rather than "dude, you are sooo hot, can I buy you a drink?"
If you really want to hit on girls in bars, then you should read Neil Strauss's book about "Inside the world of Pick up artists" whether you see it or not, you are looking like a PUA. (Pick up artist).
"You are a reflection of your friends (and lovers)"