what annoys me the most is when a whatever the last job you need to set up your pt goes afk while seeking, for a LONG time, without even putting up a search comment. 5-10minutes of AFK time, i'm fine with, but one time i set up a pt after asking someone who turned out to be afk, they came back and asked me why i hadn't saved the spot for them, and ended up getting all pissy because i didnt wait after i sent them a tell. It had been an hour and 45minutes.
i'm usually fine with people having stuff in MH, or needing to buy some more food, tools, maybe an upcoming spell or important gear piece, that sort of thing that takes 2-5minutes.
The muling thing also gets on my nerves, unless you were invited as say a pld to apt but then turns out your needed as your ninja/mnk/thf whatever at the same level, you should have all your gear and stuff you know you need and already have on your char at the very least before you start to seek for a party.