Like, a horror movie that instead of scare you makes you laugh more than a comedy
A lot of people think Star Wars is science - fiction. But it is fantasy.
I’m trying to understand this question a bit more. Do you mean intentionally not typical for it’s genre, or unintentionally?
If intentionally, I’d go with Shaun of the Dead, though it’s actually considered part of the ‘comedy horror’ genre so wouldn’t necessarily consider it ‘lying’ about being hilarious film about a zombie apocalypse.
If unintentionally, then hands down Troll 2. You can’t piss on hospitality.
Cabin in the Woods, Tucker and Dale vs Evil, and Troll 2
The Princess Bride. The title does not at all suggest that this is a comedy movie.
Stalker by Tarkovsky. The description made it sound like a really cool sci-fi/fantasy, bleak adventure movie. Instead it was just a bunch of melodramatic philosophy. Pretty much nothing even remotely sci-fi happens.