Most people trying to be "Funny" online. I'm aware that humor is entirely subjective, and I have a very, very low sense of humor, only being amused by a few select things, but this still annoys me. Whether it's people in videos, other players in games, comment sections and live chats, etc., there are always loads of people that think just referencing a meme or saying something stupid with little to no context is hilarious.
Maybe I'm old-fashioned, but I'd rather have actual jokes and well-timed funny events rather than screeching loudly, endless amounts of the same self-deprecating jokes, referencing whatever meme is currently popular, etc.