It’s a tough road selling a product whose potential side-effects are surliness, aggression and a decreased ability to communicate.

So it’s no surprise that bartenders are particularly eager, frothing like Guinness heads, when asked about the most aggravating habits of their patrons.

Lesson 1: Hold your horses

The reality of the bar is that you might have to wait a while. Just be polite: Don’t shake your drink when it’s empty like some carrot in front of a donkey, ice cubes clinking, with an aloof stare on your face.

The same goes for smacking the counter or, perhaps worse, snapping your fingers. Unless you have the Spirit of Ecstasy for a hood ornament, don’t ever snap at anybody for anything.

“Snapping, shaking your glass — that stuff used to bother me, now [I’ve realized] you’re just trying to get my attention,” Stub and Herb’s bartender Emma Collins said.

Just because Collins has come to that realization after 10 years in the industry, there’s no excuse for bar-goers in a hurry for a libation.

So what if you can’t even tell them what you want? Unless the server is clearly yukking it up with someone about nonbusiness-related topics (or checking their phone or zoning out), don’t interrupt.

“Let me finish. I know it can be busy, but I’m talking to another customer,” The Library Bar and Grill’s Kelsey Biser said.

Lesson 2: Pay as you go, sign of a pro

If you’re going to go out, shell out. Tip for every drink. All too often, younger bar-goers think it’s okay to tip every other drink. It’s a dicey practice — the next time they go up to the bar, there might be a different server who doesn’t know or care about your mighty scheme. The gratuity should be paper; a buck a drink is pretty good protocol. If it’s an elaborate ordeal with mixing and umbrellas, tip more. Even if they’re just popping the top on a tall boy, avoid solely coins — it looks tacky, even if it’s a dollar in quarters.

Lesson 3: Nobody likes you

How are you going to impress the charming bartender of your dreams? You won’t.

Go out, and you’re bound to see someone hitting on the staff, but that doesn’t mean that it is okay. Remember that being nice because it’s their job in the service industry is a lot different than wanting to go home with you after their shift.

“There’s always going to be … something happening,” Biser said. “As a server you need to be really adamant about [turning them down].”

And as a customer, you need to be really adamant about not biting the hand that feeds you (or pours your drinks).

Lesson 4: Group love (or hate)

When you are out with your cronies, know what you are going to order and how to order it.

“I hate when it’s really busy, I’m going down the line, I get to someone and they don’t know what they want,” Blarney Pub and Grill’s Emily Marshall said.

Just as bad is when people know what they want, but it’s something different for each member of a large group. This is especially poor taste when there are multiple orders for single mixed shots, like a Water Moccasin. It’s a real pain for bartenders to mix just one at a time, so maybe get a friend to do the shot with you.

Similarly, you aren’t doing a bartender any favors by letting them make one drink and then ordering another: order all at once.

It may sound like a trite executive management training slogan, but the key to all things at the bar is communication. Keep in mind that the customer isn’t always right.

Extra tips

-If you are leaving a cash tip on a card, don’t write $0.00 in the gratuity line as though gleefully not tipping.

-Don’t expect bartender friends to hook you up, and certainly don’t pester them about it. If they’re really your friend, something will probably happen in your favor anyway.

Training-ground bars

With more space and a younger clientele, these spots are comfortable for people who might not have decades of bar experience under their belts. Test out your etiquette in these youngster-friendly joints:

-Whitey’s, 400 E. Hennepin Ave., Minneapolis

-The Rail Station Bar and Grill, 3675 Minnehaha Ave., Minneapolis

-The Blue Door Pub, 1811 Selby Ave., St. Paul

Veteran bars

Other bars are tricky, with the brow set so high or low that you might not know how to act. These spots aren’t for the greenhorns, so save them for when you’re ready to be a surly regular or a black-tie big tipper:

-Champion’s Sports Bar and Grill, 105 W. Lake St., Minneapolis

-The Living Room and Prohibition, 821 Marquette Ave., Minneapolis

-Country Bar and Grill, 3006 S. Lyndale Ave., Minneapolis