Though I don't play it much anymore, I'd have to say being in first place for like the whole race, and then in the final stretch, someone passes me....
Then there's someone passing the lightning cloud onto me last minute, so I get shocked with it !!!
Then there's falling off the edges of a track when I shouldn't have, or by someone bumping me off.
Then there's throwing my item forward, and running directly into/being knocked into it.
Then there's getting useless items after I get owned by other racers, and dropped into last place...
Then there's losing my current item to a lightning bolt, or Pow Block.
Then there's getting crappy items throughout the whole race, no matter what place I'm in...
And lastly, there's Track hazards galore that I can hardly ever avoid completely...
Now do you wonder why I don't play anymore !?