Most of the words/phrases selected for this thread come across as very childish and jar with the perception of the site being peopled by intelligent, professionals which is possibly why they irritate so much.
A few things that drive me mad:
Naice
Vair
Boob/Boobage/Boob to sleep/On the Boob
Large of Nork
Veggies
You/your (whoever) is in FOG, that's Fear, Obligation, Guilt. I'm pretty sure the people who trot this out are not qualified to do so and have either just read it on here previously or on the internet somewhere and want to be the first to post it thinking it makes them sound clever.
Agree with the poster about the competitive "What are you having for dinner" threads, it's always loads of veggies or a massive salad, I bet they are actually having chicken nuggets, chips and beans.
The virtual buffets/parties. When I first joined MN several years ago there were threads upon threads full of:
"Waves to X", "Plonks large arse next to X on the bench and hands round chocolate digestives" "Starts mixing G&T's for everyone."
This would go on for pages whilst the OP and whatever the subject of the thread was were completely ignored.
Thankfully, it doesn't happen very often now.