My favorite is where, on official, I was running around on the beach on a Rex, took a chomp out of, what I though was a wild, Raptor. I stopped when I realized it didn't chase me and hopped off my Rex as a guy ran up. I go to game chat and he is screaming, "What are you doing?!" "I'm taming down the beach!" I say, "I'm sorry it was a mistake and I'll give him stuff." Next thing he says is, "Oh, youre a girl...nevermind. It's all good," and walks away.
My second is I was running around on a very high level wolf I'd tamed back when the Island was the only map. I came off a cliff into someone taming a Rex (couldn't have seen them or stopped before I jumped on them). He got onto his other Rex (medium level) and bit me twice, I went to game chat, said I was sorry, explained what happened, and what's he do? Kid gets an attitude, says he'll kill me and my tame; so happened I was next to base where 4 of us were on. We all grabbed out 150-170 Rex's (back when 100 was the max you'd find) and walk over. He keeps yelling saying he'll kill us and everything so we kill him, his tame, and the Rex he was taming. He didn't realize we were the Alpha tribe. Poor kid. Never saw him again.
EDIT: Also, back when scorched came out and people were learning about the Wyverns, a tribe mate was going to pick me and my Camel up when I got attacked by a Mantis. He hits the lightning breath to kill the Mantis and killed my Camel too. RIP Pack Muel.