While out today I thought of one!
Years ago, we were shopping for a new kitten (yes, in those days we frequented pet shops... we were young and foolish). Anyway, we fell in love with an adorable white/tabby mix, and relay that to one of the store workers. He walks over to the cage, confirms which on the two we want, gets a pet dish, and (to wake the kitty up), BANGS as hard as he can on the cage for a good ten seconds. My nerves were jangled, I don't know about the kittens'. (This was the point where we wish, and continue to wish for years, that we just got both of them).
So at this point, we just want to buy the kitten and leave. We get up to the front, and he gets a cardboard box and uses a big cutter to start punching holes in. While doing this, he turns to his coworker and says "This used to be a lot more fun 'till they stopped letting us put the cats in first!" I have never been so quickly nauseated in my life. I wish I could say I walked right out, but sadly I didn't. I like to think that it meant that I saved that kitty (who would go on to become our sweet, darling Mitsi) a lot of grief.
I never darkened the door of that shop again, ever. Months later, it was gone anyway, with a bank in its place, and I said good riddance.