I find myself irritated with overt "mechanisms" of describing a character. Not the description itself...but the mechanism used. Which isn't to say they can't be done well...I'm just a cynic about them. It could be mirrors, photographs, or some alternate POV character giving the main a once-over. I also find myself irritated when some trait of a character is described in loving detail, and is supposed to make them hot or attractive or something, and I don't find that trait particularly appealing. In urban fantasy you run into a LOT of stories where a character is attractive due to their body alone, usually for stereotypical reasons, and are never fleshed out very much beyond what they look like, or given an "odd" body type, or whatever.
That said, what is worse is getting halfway through the book as a reader, and discovering your mental image in no way matches with the character. There's one or two cases where that might be the POINT of the story, but outside of that, I don't like thinking a character has, say, green eyes and curly red hair only to find out they really have straight black hair and brown eyes.
I'm far more forgiving about narration that gets in there, gives a description, then gets on to the next thing. If that makes sense. Like, I would prefer the narration points out they have black hair and orange eyes, and moves on, than the author setting up a scene or "mechanism" for the sole purpose of describing a character.