Guess I'll be the first one to say Maple Treeway from MKWii. No matter how well I do on it, something always seems to go wrong. The Wigglers, the wavy net, you name it. Anything that can go wrong for me on Treeway has gone wrong.
I also dislike Luigi Circuit. Luck truck. Need I say more?
MKWii's Rainbow Road is frustrating too. The game's physics are bad enough as is, but this track takes that fact to the next level. Also, if you get knocked off when going down the hill at the start, you get spawned back at the top of the hill and you better hope you don't get knocked off again. I actually wait for everyone to pass me at the start of every Wii Rainbow Road race just so I don't get bumped off. The penalty for falling off there is too big.
Mushroom Gorge (Wii version) is awful too. It's so boring, doesn't require much skill, and if you get knocked off, blued, or shocked off at the wrong spot, you get a terrible respawn. I've never liked this track because shock or blue shell at the wrong spot can ruin your race, even in a room with lesser skilled players.
Next, Grumble Volcano from the same game. Now I actually like this track in MK8 because I feel that it fixed a lot of problems it had in MKWii. The thing that ruins it for me in MKWii is that rock glitch that everyone loved taking so much. I would actually go out of my way to block the glitchers. That's how bad it was.
GCN Peach Beach sucks too. My luck here sucks too.
Same thing goes for GBA Shy Guy Beach. Second worst luck track in my opinion. The water is not fun to drive on, at all.
GCN Dry Dry Desert is another track I despise, both versions. It's too slippery, the tornadoes were annoying, and that shortcut at the end is way too powerful.
Finally, GCN Baby Park. Worst track ever. It's way too chaotic for my liking and that makes it really unenjoyable for me.
I seem to dislike a handful of GCN and Wii tracks, lol.