I don’t know if this belongs in this sub but here goes. This happened to me about 5yrs ago.
So I (Me) was standing alone at the edge of the dance floor at a bar my roommate was DJing, just enjoying the music and sipping a beer, when some girl (SG) comes up to me and starts a short conversation: SG: hey how’s it going? Me: pretty good, just enjoying the music. How about yourself? SG: I’m doing well. This music is great, isn’t it? Me: Yeah it is, my roommate is tonight’s DJ. SG: that’s cool! Wanna get a shot?
Now at this point I’m pretty happy; this girl seems interested in me, and she might even be offering to even pay for mine! Obviously I wouldn’t be telling this story if this was the case, however. And here’s how the rest of the encounter went.
She leads me to the bar and introduces me to her friends, they all seem nice.
SG: so what kind of shot do you want? Me: a shot of Jameson. SG: (to the bartender) we’ll have 6 shots of Jameson.
At this point I realize exactly what’s about to happen but I’m still hopeful that SG is a nice person and not trying to get one over on me. And in either case, I know what I’m about to do.
Bartender: (delivers us the 6 shots) that’ll be $40. SG: (pauses and then looks at me) aren’t you gonna pay for them? Me: Nope (I take my shot, turn 180 degrees and walk back to where I was standing before).

It’s common knowledge that if you ask someone if they want a drink, then you are offering to pay for both drinks or at least your own.

TLDR: SG thought she found a mark that would pay for shots for her group of friends. She and/or her friends end up paying for all of their own shots, plus mine.