I have played probably the world's most annoying stage.
It's actually called "The most annoying stage ever!!!!".
B028-0000-0078-3F97
The main reasons why it's so annoying:
1. It's an automatic/don't move/don't press anything level (which some people find annoying)
2. It's not completely filled, but it does contain some annoying SFX (especially at the end).
3. This is THE most annoying part. It's automatic... but you may or may not complete the stage. Sometimes, Mario will successfully get to the goal post. Sometimes, he won't. When he does, you will most likely have 7 seconds left. The reason for this, is .... actually I don't know <_<.
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If however you want a not- so annoying stage, but one that's just hard.... but not anywhere near Kaizo:
D3E3-0000-0057-B313 (Hard But Fair).
The only unfair part, is an arrow of coins leading to an area, in which you are immediately greeted by a Bullseye Bill Blaster, that shoots a giant winged fireball (which moves VERY VERY fast..... almost as fast as Mario running on a conveyor belt at full speed). Just run as soon as you see it. That is, if you don't take the not-so-secret pipe, leading to a chase with Bowser on reversed conveyor belts (i.e. you are running against the direction of the belts so it's slower), combined with explosive Bob-ombs walking/running towards you.
Most of my stages however, are just for lulz.
1818-0000-003A-6CFC (Don't Stop)
Basically, a full-speed 12-screen conveyor belt run, with a few enemies running towards you. The speed makes it relatively hard. Just make sure to get the star. Otherwise, the end is impossible. Or just very hard.
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And for those who hate those annoying stages in the Expert mode where you are immediately greeted by enemy spam with no room for error....
F6DB-0000-0059-652E
The screenshot may put you off, but .... you'll start invincible. It's kind of to make fun of enemy spammers... but also give you a stage that looks impossible, but is incredibly easy.