I am really sick of people never replying to emails.
I'll go on craigslist and send someone an email....and state that I am interested and would like to buy whatever it is, and they never reply.
It is REALLY aggravating. And other times I'll be just talking to someone via email about something I or they have for sale and we're just about to make a deal and then boom, never hear from them again. It really ticks me off.