Not that I look for lemons most of the time, but I hate running into a bunch of them looking for romance. I also hate that out of all the parings I support I only run into them for one of my 'ships. And there always Plot What Plot. Kigo apparently has a good following why can't I run into one for them? Or Ash and Misty?
I don't mind sex in my fanfic, but what annoys me about the more explicit varieties is the tendency a lot of writers have to use really creepy, weird euphemisms, and that's why I avoid lemons as a rule. I once unwittingly stumbled across an ATLA lemon where someone's penis was described as his Unagi◊... Ewwww.