A recent magazine survey, interviewed fifty bartenders and they were asked if they could identify a customer's personality on what drinks they ordered.
Although interviewed separately, they concurred on almost all counts.

The results:

IF WOMEN DRINK....

Beer.
Personality: Casual, low maintenance; down to earth.
Approach: Challenge her to a game of pool.

Cocktails or Blender drinks with umbrella.
Personality: Flaky, annoying, dizzy, and a pain in the ass.
Approach: Avoid her, unless you want to be her cabin boy.

Mixed drinks - no umbrellas e.g.; Scotch and soda.
Personality: Mature, has picky taste; knows what she wants
Approach: If she wants you, she'll send YOU a drink.

Water.
Personality: Pretentious and is looking for a serious relationship.
Approach: Don't.

Wine - (bottled, not 4 litre cask).
Personality: Conservative and classy, sophisticated.
Approach: Try and weave Paris and clothing into the conversation.

Bacardi Breezer, Red Square, Archers Cooler, Smirnoff Ice, etc.
Personality: Easy; thinks she is trendy and sophisticated actually has absolutely no clue.
Approach: Make her feel smarter than she is... and you're in.

Cape Velvet.
Personality: Annoying voice, bit of a tart.
Approach: Stand close and mention the alley next to the pub.

Shots and Slammers (Tequila, Vodka, Aftershock etc.)
Personality: Hangs around with male work pals or looking to get drunk and naked.
Approach: Easiest hit in the pub. Nothing to do but wait.

IF MEN DRINK... (As always, very simple and clear cut.)

Cider: He's probably under-aged and wants to get laid.

Cheap Domestic Beer: He's poor / student and wants to get laid.

Premium Local Beer: He likes good beer and wants to get laid.

Imported Beer: He's old; he likes good beer and wants to get laid.

Guinness: The man is a chancer and will get laid one way or another.

Water: He just threw up and is trying to wash the taste out of his mouth so that he can still get laid.

Wine: He's hoping that the wine thing will give him a sophisticated image and help him get laid.

Vodka or Brandy: Extremely horny hound, would shag a warm scarf.
Desperate to get laid.

Port: Thinks he's sophisticated, secretly likes men and wants to get laid.

Whisky: He doesn't give two $hits about anything and will hit anyone who will get in his way of getting laid.

Jack Daniels: Not as masculine as the whisky drinker, knows all about feminine activities (knitting, crochet etc.) to weasel himself into getting laid.

Rum or Tequila: Likes fighting almost as much as getting laid.

Bacardi Breezer, Red Square, Archers Cooler, Smirnoff Ice, etc:
He's gay (blatantly) - don't turn your back or pick up any dropped change.