Well, I don't like how the Red Shell being a homing device, Dry Bowser, the Blue Shell's entry, Dry Bowser, the lightning's nockoff, Dry Bowser, Dry Bowser.
He's just too fast. 
Oddly, I've never had problems with Dry Bowser. On the Wii, the main annoyances are usually Peach or Donkey Kong. I play as Toad, one of the lightest characters in the game, so...
Now, in Mario Kart DS... I swear to God, R.O.B. was programmed to just murder the player. If he's one of the two usual rivals at the top of the standings, he's always on your ass with red shells. If he's buried in sixth, he's packing blue shells like crazy. It's ridiculous.