People go to bars for various reasons, and one of the chief purposes of a trip to a decent cocktail lounge can be to meet other like-minded people.
Don't make the mistake of pushing yourself on others, though. If you feel unwelcome, chances are they don't want to be disturbed.
If you want to send a drink to someone you don't know, the way to do it is to ask the bartender if she could ask the person in question if that sounds like a good idea.