Snowbladers (AKA. snowlerbladers). One of them caused me tear my ACL. They are a scourge on the mountain.
People who stop for no apparent reason in the middle of a run, usually when I am going about Mach 10.
People who stand on my skis in the lift line. The occasional step I can handle, hey, it's a crowded place. But those morons who simply stand there grinding their edges into my lovely topsheet deserve to be stabbed with a ski pole.
Give me some time, there will be more...