By Jove, These People Are Idiots.
Case Study #1:
"There are adults who ask me what I want to eat, and I tell them anything without meat and they say, "oh, tee hee, well all we have is hamburgers! You'll just have to eat that!" and I'll say "That really isn't funny." and they'll be all "haha!"
Since these people are adults, you really can't hit them without incurring their wrath (and that of your parents), which really sucks. So...I'd say something like "Or maybe I can just eat you. You're dumb enough to be a cow." (no offense to the cows) With luck, they won't understand that you just insulted them. To be on the safe side, run.
Or, to be on the safer side, say something more along the lines of "By jove, we have a jester in the house! Can I have some of that potato salad?"
Case Study #2:
"People at lunch have the need to tell me "Look! I'm eating meat! Hahaha!"
Since these people are your friends, you can hit them. Or say "Look at me! I'm not! Hahahaha!"
Case Study #3:
"I was hanging out with a couple of my friends, and they were both wearing leather jackets. I mentioned, like, jokingly that I'm a vegetarian and the fact that they were wearing leather bothered me. So, right away, one of them starts shoving the sleeve of his jacket in my face."
As it says on the dealing with jerks page...this is not funny, and it never will be. HIT HIM. If you can, destroy the jacket too.
Case Study #4:
"I was shoe shopping with my mom, and she was looking at these shoes that had this snake skin pattern and the conversation went something like...
Mom: I hope this is fake.
Me: Why?
Mom: Because if it was real snake skin I'd feel guilty
Me: But...you don't have a problem with leather shoes...
Mom: I know. "
It's quite obvious...she just has no clue. Seeing as this person is your mother, best just let this one slide. Heave a sigh so she'll see that you're exasperated though. That's always kinda fun.
Case Study #5:
"We were at a Chinese restaurant and she tells me that I might get an eggroll with my meal and she says
Mom: Well, they're mostly made without meat
Me: Mostly?
Mom: Well, they might have shrimp
Me: Mom...I don't eat meat...I don't eat shrimp...this isn't new.
Mom: But most people don't consider fish meat.
Unfortunately, this is the same as #4, she just doesn't get it. There's not a whole lot you can do but be patient and hope that maybe she'll get it if you repeat yourself enough times.