A couple of veterinary-specific ones:
1. Yes, you will have to pay. Tonight. I know, I really do, it sucks for everyone to have a big vet bill-and at the ER it will probably be big-sprung on you. Please, please, don't yell at us that we're just in it for the money. Especially these days, the staff you're yelling at has likely had their hours cut, they live in fear of being laid off, and their employer had to scrape to pay their vendors last month.
2. Please try not to bring your pet in when you have been heavily indulging in mind-altering substances. Yes, OK, that's some people's idea of fun at 2 AM and I'm not here to judge you, but drunks and stoners have a hard time making decisions.
3. Don't call us first, describe your pet's symptoms, and argue with us about whether you really need to bring it in. You called me, dude. Unless it's something extremely simple, that's what I'm advising.
4. We are not Animal Control. Don't call us to come get a stray. And don't you dare abandon an unwanted pet here.
5. Knock it off with the prank calls. We're busy here.
6. Please don't make me explain everything to you, then call your spouse and hand me the phone and make me explain it all over again.
7. No, I'm sorry, you can't sit next to your pet's cage in the treatment area. I've tried it and it was a crippling distraction.