Things that irk me:
"Please read and review!"
"This is my first fanfic!"
(Seen on fanfiction . net - a good way to guarantee that I won't be reading. As real world literary agents say: "Don't tell us this is a first novel" on account that it's natural to assume anyone's first attempt at anything is bad).
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"tl:dr"
"I didn't read this, but..."
(I *despise* comments that only serve to tell everyone that someone was too lazy or too stuck up to read something but has an opinion, anyway. Typically, it's an opinion that can be crammed right up their rear).
I have another quote that's an actual quote from somewhere that I see too often in places other than here online that annoys me, but to even post it would be Mature Discussion material and I do not feel like re-instating myself into that forum for it.