If you want to get girls to like you, you can’t just be likable. You have to practice. You can’t just practice in the mirror because the mirror will love you, but the world won’t.
Start with places where you buy food. See what works and what doesn’t. Try your cute mannerisms on the woman (or man) behind the counter. If you’ve got new material, this is the place to try it. If you’re wearing jeans, casually put your left hand in your pocket. See if that garners any attention. If it doesn’t, try the right hand. Ask her how her day is going. If she answers unfavorably, it’s either because your question isn’t working or because she just hates her job. If it’s the former, try to revise your question the next day. Go for minimalism. Just say, ‘hi’.
For the lady working behind the counter at dinner, take another approach. Be the over-confident guy. Hold up the line while you continuously talk to her, whilst never taking your eyes off hers. When the guy behind you tells you to move, defend your honor! Show her that you’re not a pushover. Ask her out in front of all of the angry people behind you. Sure they will roll their eyes, and may spit on you, but it will be spits of respect.
Do this so much that it becomes second nature whenever you’re in public. I don’t see any potential drawbacks to this at all. Don’t necessarily hit on every girl you see. Just work out all of your quirks and pay attention to what works. The absolute worst that can happen is that you will alienate everybody in your life and will die alone.
However, do not practice your flirting at work. This is dangerous, and really is the best literal manifestation of a lose-lose situation. When you get rejected, you lose a date. When you get rejected at work, you lose a date and a job.