Keep your bartender company on slow nights
Do talk about: sports, music, movies, drinking, embarrassing sex stories, “ancient aliens”.
Don't talk about: politics, religion, how much money bartenders make, sex stories where you’re really good at sex.
Don't freak your bartender out on slow nights
If you're a creepy stalker, just be low-maintenance about it. Bartenders of both sexes know they’ll have admirers. If they think “I can live with this creep” instead of “I’m calling the cops on this creep”, you’re winning (relatively).
Be respectful even when you feel you’ve been horribly wronged
Bad-tasting beer is rarely the bartender's fault, and regardless he'll comp you a replacement -- happily so if you're cool. If you got the wrong cocktail, you might have ordered wrong, especially if you ordered for a group. If you got the right cocktail but think it was made wrong, remember that bartenders dip a straw for a taste before serving. If the drink’s truly off, they’ll catch it.