Waiting for the glue to dry on props. Since I am in-charge of most of the props for my cosplaying group, I can stand waiting when it comes to paper mache', but glue? Must be dry as soon as I put it on. Grr.
Oh, yeah, and redoing weapons when you have to nearly rip them apart, without ripping them apart, stinks like non-showered cosplayers on the last day of con.