"I don't really like this pairing, but I decided to give it a try" when it's followed with "And this didn't really change my mind". Oh, really? And you think this is worthwhile for the writer to know because...?

Historical/cultural nitpicking when the reviewer is wrong. Especially if the reviewer's tone is condescending and know-it-all.

For that matter, nitpicking about how something is OOC or incorrect when it's straight from canon.

In-depth concrit on kink memes.