Neil deGrasse Tyson estimated that if you collected every beer coaster, cocktail napkin, and bar tab on which someone scribbled their number for a bartender, they'd stretch to Jupiter and back a thousand times. Flirtatious customers are about as ubiquitous as Miller Lite for bartenders and servers. So if anyone knows how to flirt the best way, it's bartenders, right?

We talked to a bunch of servers and bartenders, who offered several general tips, as well as how to flirt with the bartenders themselves. Here are their best flirting tips:

1. Don't bring up anything sexual.

"Even if the server or bartender picks up what you're putting down, always assume it begins and ends with flirting. ... Restaurants and bars can be sexy environments, but we're not sex workers. We are not obligated to respond in kind. Stop flirting in front of your date, and for God's sake—no touching." – Liz, Brooklyn

"Being super friendly is awesome. Making friends with people who work at your regular spots is also awesome. But while in the bar, don't mention anything sexual. Don't even comment on the server or bartender's looks. They are at work. Respect that." – Emil

2. Be respectful...and don't call them names.

"Never refer to your bartender as 'sweetheart' or any other overly familiar form of address. It's not flirting. It's condescending." – Anonymous

"Be polite and cognizant of the fact that they have other patrons to tend to. ... Leave your number, but don't ask for theirs. Definitely do not ask what they're doing after work." – Sydney, Chicago

3. Don't force things. Keep discussion natural.

"It is important not to have any expectations other than a good conversation. Just don't force anything. That turns creepy really quickly." – Stephanie, Edinburgh

4. Make Eye Contact.

"Eye contact means everything." – John, Cleveland

5. Notice if their body language responds positively.

"There's nothing wrong with flirting, as long as he or she knows there are boundaries that must be respected—this includes being able to aptly read any verbal or physical cues the bartender is broadcasting regarding his or her own comfort with the situation." – Mark, Chicago

"If they check on you more than usual, [or give away] a free shot or drink. If they look at [you] while taking care of other customers." – Rebecca, Chicago

6. Notice if their body language responds...less than positively.

"There's nothing wrong with complimenting someone. ... If the bar patron, however, takes it one step further (i.e. 'Wow, you must work out a lot,' etc.) and said server or bartender doesn't reciprocate, obviously that's [a] problem. – John

"If the bartender is being courteous but keeping a bit of distance, said individual isn't warming to your song. The best measure I know of is body language." – Mark

"If you're questioning the intention, then the answer is likely no." – Stephanie

"If they're making the kind of small talk you'd have at a bus station, they aren't interested." – Sydney

7. If you're flirting with the bartender, let them do their job.

"Never expect a bartender to flirt if the bar is busy. Bartenders are there to do a job, not to stroke egos or pursue romantic liaisons." – Mark

"Just go for it, but don't get too upset if said bartender or server is too busy. They may be interested but actually care about doing their job. Don't take it personally." – James, Brooklyn

"It is 100% always the server or bartender performing their job until THEY prove otherwise. They will make the move. If you want to leave your number to be proactive, cool. Let them call if they want." – Liz

Some of these quotes have been edited and condensed.