Pet peeve number a zillion: when I'm trying to tell someone something and they try to leap to the end instead of letting me get there. Bonus irritation if it's funny or unexpected and they try to jump to the punchline.

"-so around three am there's this scream, and I-"
"-oh so what, it was a fox?"
"Okay Clara so we'll skip the funny bit entirely: my neighbour screams loudly at night. I'll tell someone else the longer and much funnier version that involves me accidentally-"
"-oh what you called the police?"
"NO"