Someone else: "Speak English! LOL!"
Pisses me off, every single time. If people are having a conversation, and you're not educated enough in the topic to contribute usefully, then either ask useful questions to educate yourself, or keep quiet until a conversation comes along that you _can_ take part in.
Leaping in with "I don't understand complicated things, but still feel that the conversation should be all about me." is annoying, childish, and was mildly funny the first time I encountered it, 30-odd years ago.
Oh God, I'm a grumpy old man.
Original post on Dreamwidth - there are comments there.