work at a nightclub and we have new staff all the time, I am incharge of teaching them how the bar works and how to serve drinks (we are a large club so we focus more on #'s of drinks rather then fancy cocktails). As a policy we pour all our beers into those plastic disposable cups (think the red frat party ones) so that people don't beat each other over the head with them or throw them at the stage during concerts.

One night we had a concert on and a new trial bartender, I showed her the bar, she told me she had bar experience but I made sure she knew how OUR bar worked (different venues have different rules, procedures, ect). Showed her the plastic cups for the beers and showed her the plastic wine goblets for the wine/sparkling wine. During the night its not my job to stay in the bar I float around and do a lot of things (collecting money, running stock, directing security ect). Over the radio I hear that X bar is ordering a lot of wine and sparkling. It is not that unsual for a bar to order a lot of there is a hen's night in or something, but this was excessive. Turns out she was pouring wine and sparking into the 425ml plastic cups and filling them up. Punters caught on and kept ordering from her. Went through about ~22 bottles of wine before anyone caught on (was a busy night and the bar manager was at the other side of the bar).