The one time that stands out in my memory was this. Not because it was the worst, but because it was so absurd.
In senior year of college, there were maybe 11 or 12 classmates in my department and on some Thursday nights we would all get together, go up to one of the bars up the hill, and drink and talk about our theses. It was more of a cocktail hour than anything, because AFAIK the most anyone ever had was three beers over as many hours.
So one night we're at this bar for maybe 1.5-2 hrs, and some of us are going to head back down the hill and get back to work. I have had exactly one weak ginger drop cocktail. My debit card (my only source of money -- didn't have a credit card or carry cash back then) was with my tab. I went to settle up but the bartender who had started my tab had gone off shift (and home) and the current bartender INSISTED that if the previous bartender had my card to start a tab, then he would never have taken it away from the bar.
She not-so-subtly accused me of being drunk and trying to stiff them. !!! Over a $5 cocktail !!! She just would not accept that maybe he slipped the card into his jeans and forgot, and she wouldn't call him either. (It was only 11 then, and he had just left to go home.) After some uncomfortable words where I maintained my stance that I absolutely gave this guy my card, she takes my number and says she will call tomorrow when he comes back on his next shift (this was my suggestion, not hers) and I just leave. Mind you, I am sober, worried, and slightly panicking because my debit card had been stolen the year before.
Next day at 1 PM: I get a call during class, and after class lets out I check the voicemail. Sure enough, guess where my card was?! My boyfriend drives me up the hill between classes. Both bartenders are there. Dude bartender who took my card home doesn't even acknowledge my existence or what happened. The female bartender is still being rude with me like it's my fault that they lost my goddamn card. I get my card, pay for this stupid cocktail and tip, and never return.
The false accusation of being 1) drunk 2) dishonest and trying to squirm my way out of a $5 bar tab and 3) somehow inconveniencing *them* just pissed me off. That bar (and its attached restaurant) were known for being rude and just generally having bad service, but I had never experienced more than standoffish bartenders until then.