For some players, holding onto a blue shell can turn into this. The lead cars will often panic and stop dead in their tracks.
In Wii, playing as a regular character or as a Mii and seeing your own Miis in Coconut Mall is pretty hilarious as well. Especially since they also drive the parking cars that you must dodge at the end.
If you play as Wario and he gets lower than Sixth place, he will loudly grumble, "I hate you."
In Wii and 7, if you rank low enough, Bowser will grumble out a coherent "Horrible..." One of the few moments in recent years (Outside of Bowser's Inside Story) where he actually talks, rather than just roaring and grumbling.