How do you surprise a blind man? Put a plunger in the toilet.
Blind Man's Surprise
Explanation
Explain Bear
Listen up, buttercup. The joke is funny because a blind dude can't see the plunger in the toilet. When he sits down, he's gonna get a nasty surprise. It's dark humor because it's about messing with a disabled person, which isn't cool, but it's kinda funny if you're a terrible person.