If there's definitely one type of roleplayer that pisses me off more than any other it's people who show up to a roleplay. Show interest, and even go to the OOC. Then drop out without so much as a word unceremoniously. It's bullshit. It's especially disrespectful to the gm who's going to be expecting you to be in it. Like it is so god damn asinine that you can't even drop a comment, OR A PM to someone and let them know you're not interested anymore. 

It's the equivalent of signing up to help a charity, it's free, and only requires you to put some effort into it...and then not coming to your shift.