Toad's voice in Mario Kart 64.
Most enjoyable moment in Mario Kart games: Hearing Toad scream.
Seriously, I hated how in Super Mario Kart the computer had access to weapons you didn't have (like Yoshi dropping eggs). In Mario Kart 64 I hated when someone used a lightning bolt right as I was about to cross the big jump in Wario Stadium. I never slowed down, I just accepted it and failed to leap over the chasm instead of turning back and getting enough room to fly over it when I returned to normal. Not sure if I would have saved time that way. And no matter how you sliced it, Rainbow Road for Super Mario Kart was annoying for not having any rails. Of course, I never played through the game normally so I wasn't prepared for skidding effortlessly through the track, but still.