Leave chewed-up straws and torn coasters everywhere
You are either nervous or part-hamster, and because of you, bars are littered with remnants that make it look like they were attacked by booze-crazed rats. Somebody has to pick them up, which sucks because nobody wants to touch spit-covered anything.
Snap or whistle
You snap and whistle at your dog. Your dog thinks you are an a-hole. Imagine how the bartender feels.
Turn the bar into a sex hotel
Making out in a bar is one thing. Making out at the bar
is quite another... especially when the bartender has to discern an order you're making with somebody else's tongue in your mouth.
Ordering bartender's choice
When it's not too busy, it's never a bad thing to go omakase at a bar. But when the place is slammed and you don't know what you want, just hang back and make a choice. Forcing a busy bartender to make it for you is gonna get you a shot or, even worse, a watered-down gin and tonic
Step behind the bar
Some people get so comfortable with the bartender, they'll actually cross over to the other side to place an order. Don't be this person. Ever. You are crossing into a special place from which you are expressly forbidden.
Order a tall drink, then complain that it isn't strong enough
Tall means more mixer, not more booze. Don't surprised when your drink tastes more like Coke than rum… and next time, order a double. Or just not a rum & Coke. Or both!
Be shocked that this bar doesn't have what the last bar you were at has
What? They don't have that delicious 30yr-old Scotch you had at the upscale bar earlier? Of course they don't. You're at a brewery.
Order one drink at a time
If you're ordering a shot of tequila, a mojito, two beers, and a chocotini at a busy bar, order them all at once. Don't wait for one to come, then order the next. And the next. Most bartenders have two hands. Bartenders who don't have learned to adapt.
Scream out your order
Bars are loud. A good bartender has learned to tune out the noise and read lips. That's why she's gonna be pretty perturbed when you lean in close like you're gonna kiss her, then scream your order in her face.
Be impatient about a wait, then don't know what you want
This specimen of bar amateur will stand at the bar and loudly scoff every time another patron gets to place an order before him. Then, when the bartender finally gets to him, his grimace turns to a blank face, and he has no idea what he wants.
Horribly dominate the jukebox
Look, your love of Semisonic is yours to share. But when you toss $10 in the jukebox and play their Greatest Hits album straight through -- twice -- you're also basically doing the musical equivalent of Chinese water torture to your barman. Also, does Semisonic even have a Greatest Hits album?
Graze the garnish
The maraschino cherries, olives, oranges, and lemons are drink garnishes, not buffet items you should contaminate with your gross fingers.
Close a tab, then start a tab
Sure, maybe you changed your mind about that last drink and opened another tab. It was fine until the fourth closed tab of the night. Now you're just wasting paper, and racking up charges for the bar, and generally being as annoying as possible. You shouldn't have used all your cash to play "Closing Time" four times in row.
Say, "I'll tip at the end".
Yeah, we know you will. You'll order expensive, complex drinks all night under the pretense of, "Don't worry, I'll take care of you before I leave". Then you'll order a $3 beer, leave a buck, and call it good.
Complain that your 3/4-finished drink is wrong
Did you seriously not realize that your Manhattan was actually a White Russian until it was almost gone? Usually, a bartender will gladly rectify a mistake. This is not that time.