If i deem to spend my hard earned cash on a "premium" lager, say Peroni, then at circa 4.20-4.50 per pint i expact it in a Peroni glass, as they are designed to enhance the drinking experience of the product, not some overwashed scabby struaght sleever. You'd be pissed off being served champagne in a slim half pint tumbler after all. As a rule the consumers in this country settle for farless than our contempories in the States.
Space is finite, sometimes a bar will run out of clean peroni glasses as it's 'the lager to be seen with', they also lack a certain structural integrity and often break easily, of course people often steal them too.
It's illegal to serve in other branded glasses so there will always be a stash of regular glasses on hand as they can be used for anything and take up far less space than their non-stackable compatriot peroni glasses.
We in the industry would love to be able to serve 100% of drinks to spec because most people take great pride in their profession, alas it is sometimes out of our control.
I would always tell the customer first in the case you mention to give them the option of choosing something else, if this isn't happening that is a problem.
Some bellend in a restaurant overcooked my steak today, so much so that I left some of it. I am now really annoyed at myself for not saying something.
Always say something at the time mate, I actually quite like dealing with complaints as I believe in people getting what they pay for and I like it when an otherwise unhappy customer leaves happy.
It's way more preferable for restaurants to deal with things straight away rather than face a bad review after a customer who has said nothing during their visit subsequently puts something on trip advisor for examlple. If the restaurant deals with your complaint badly then take them to the cleaners on TA.
Also tell them it's your birthday, often a free desert or glass of prosecco can be comp'd. Don't take advantage though...