having been a bartender for several years and having many many many people return beers for whatever their reasons.. it just gets old.
even if you are a great bartender, super patient and the person asking for a fresh/different drink is awesome and hot and reasonable and uses all the right descriptors.... sometimes you just don't give a **** and don't want the education...... again.
just take it back and say "let me get a replacement, chief. this one's no good"
bartenders don't want a lecture, to be told the history of the style, to be talked down to like they're morons because the customer can quote BJCP guidelines.
when you've been on your feet for 10 hours, running around like a sugared up toddler, being whistled at, having people snap their fingers to get your attention, stiffing you on tips, complaining about their wives, their ****** lives, etc. and some beernerd comes up to lecture you on the difference between stouts and porters and tells you the beer they ordered is 2 degrees too cold to be properly consumed or something.... all you want is for them to go away.
so... yeah... it happens. bartenders hear a lot and get jaded with time. we're not impressed and we really don't want to hear it.... again.