Dream Forest-Anguish lagoon: Srsly, the part where you use Moskito to fly is annoying. Especially when trying to get that one cage....
Bandland-Gong Heights: The beginning part of the level is REALLY frustrating. Those freaking monks can't keep their hands still. T^T
Blue Mountains-The Hard Rocks: Nothing too hard about the stage, other than the Electoons being really hard to find.
Picture City-Eraser Plains: Ugh, this stage really is a bite in the @$$, and the boss is pretty unreasonable.-Space Mama's Crater: OH GOD! Don't even get me started. >_<
Cave of Skops-Eat at Joes: First it's the dark cave where you cant see anything, then there's the annoying bugs that shoot heat-seeking thorns at you, then the annoying space ship area, then the giant hazardous body of water that you have to jump across, geez, Ubi tried too hard.
Candy Chateau: Hehe, the funny things is, that the last level is one of the easiest.
Rayman GBC:
Spellbound Forest-3: Yeah, the level is simple, just avoid the water. But making a mistake can be really easy, and you have to wait for the screen to get high enough for a few rising platforms, or else you fall right through it, into the water, and have to start ALL over again.
Airy Toons-?: I don't know. None of the Airy Toons stages really annoyed me.
Rainy Forest-?: Same thing with these levels too.
Rocky Peaks-4: This stage is long and confusing, and the one save point is positioned in a rather early spot.
Ancient Forest-1: OK, this stage is really easy, except for the last ring you have to jump too.
Fiery Depths-?: Another really easy set of levels.
Arcane Forest-2: The pit at the end of the second Arcane Forest level really grinds my gears.
Dark Legacy-ALL: Unlike the PS1 version, these final levels are actually hard.
) but I hated space mama's crater with all the bouncing rubbers and spikes 
