On the one hand: it’s just a drink and if it’s to be made using a self-service machine, then that’s how it is.
On the other hand: acting out of line in a job is not ok, and rudeness is not ok. Excusing it by saying “the bartender isn’t paid well” or “look at what the bartender deals with all day” is not ok, either; no matter what job we have, there is always someone who is paid more than we are, and if someone isn’t willing to do his or her best, the person should find another job.