In my experience, flirting is most effectively perceived while one is at the peak of the bell curve of intoxication. Drink too little and your insecurities will interfere with your ability to gauge whether he's flirting; drink too much and you are, well, too drunk to tell.

I second Quendalon's advice. A drink is good to relax you, five is bad because you fall over. If he's flirting with you, great! But you may have to be more direct...

I don't drink alcohol. I'm not trying to be a prude about it. I've just never liked the taste of it.

As a large section of my life has been involved in selling alcohol, I must object. Alcohol itself has no flavour or aroma whatsoever (although I would warn that telling a police officer that when they say they can smell alcohol on you through the car window is not a good idea).
I would happily rise to the challenge of finding an alcoholic drink to match any person's taste, scent and aroma preferences.
I would like to add that alcohol is an evil and toxic chemical, and if cannabis had been discovered first, we'd all be sitting around smoking pot in bars, condemning the petty criminals that shoplift to pay back-street dealers to feed their Zinfandel addictions :-)

You can object all you want. However, any time there has been alcohol in a drink, I've been able to taste it. I had a friend who was that way, too. I'd imagine we're in that group of people known as "super tasters."