Things that make me say "Nope" to a group are;
1. If the group is "Literate", but posts annoyingly long posts that I don't want to be bothered to reply to. I understand long posts sometimes in a battle but why can't people just roleplay in shorter sentences? I used to love literacy until I realized, it slows down roleplay and wastes the day away while waiting for slow typers to reply.
2. Wolfspeakers. I used to have huge issues with this, people using such idiotic terms in what should be a normal sentence, but not as much anymore. I try to ignore them nowadays.
3. Power players. The common error is that people think they mostly exist in mapless roleplays. They do not. In some of the mapped roleplays I have been in, people have powerplayed so badly that they ignore each of my posts, thinking themselves more important than what I've typed. This isn't everyone and it does seem to be a minority, but it makes me upset.
4. Groups that claim they will have a map and they never do.
5. A group with a map that takes too long to download, or the map itself is god awful. (I do like some simple maps, but by horrible I mean some textures don't work, or the entire map just looks like it was thrown together by an ametuer... I understand someone who is learning, so it isn't that big of a deal but it ruins the RP experience)
6. Groups that ask me to make a map and when it's finished they abandon it for someone elses. This happened to me at least 3 times... with three different maps.