Things I'm a huge fan of:
Plotting things, starting agreed upon threads, then having them go ignored.
Valid excuse some of the time, but one would think that after plotting, and my telling you that 'I'll have a starter up ASAP and tag you in it' means that you would, at the very least, go to my blog and look for it if you didn't see it within a day or two. I'm not here to badger you and remind you that you said you were going to play with me, I assume that if you took the care to plot something out with me, you actually want to play it. Once I start something, the ball is in your court.
Maybe it's me expecting too much of people, but if you don't want to plot with me, just tell me.
If you no longer have muse for the thing we discussed, tell me, so I don't feel like an idiot thinking I'm going to get to do something only to get ignored.
I'm not that person who's going to hold a vendetta against you because you didn't think we meshed well.
Sorry for the early morning passive aggression, but when I realized this has happened not once, not twice, but four or five times, I felt the need to say something.