I'm relatively new to this. Only been doing it a month. But but one of my pet peeve's is when CO's don't provide information for parking. Just because it's a city park doesn't mean there's parking. I know of two parks in my area that don't have parking. One I found had no parking because I went to look for caches there. After driving around looking, I simply gave up. Or what if I'm out of town and don't know the area, and I have to hunt for parking? Takes a bit of the fun out of this game.
Another pet peeve is when the cache description says "no bushwhacking" but when you get there, you need to bushwhack. Just because you didn't need to bushwhack in 2005 when you hid the cache, doesn't mean that by 2012 the area hasn't become overgrown.
Another one is when attributes are selected... kid friendly, dog friendly, but also ticks, thorns, poisonous plants, and/or dangerous animals? Really? I don't want my child or my pet romping in poison ivy. On a similar line is when the area has these things, and they aren't noted.
And finally, CO's that don't maintain their caches. There is one local (to me) CO who's caches I don't even bother to look for, because of that. It makes the CO look bad, takes the fun out of it for new cachers, and is probably quite annoying to more experienced cachers. If I look for 30 minutes or more, and can't find it because I'm new and really don't know what I'm doing, that's one thing, but if I'm wasting my time because it's gone missing (and the cache owner hasn't bothered to check/replace), that aggravates me.