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.
Could consider the Ash vs Evil Dead series to qualify. It was technically horror, but done in a very entertaining and campy (hindsight) way and not taken too seriously.
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.
Donny Darko, maybe? All I knew was that it was a psycho thriller. I had to go on the internet to find out WTF I had just seen, because it’s also a sci-fi.
The Princess Bride. The title does not at all suggest that this is a comedy movie.
Cabin in the Woods, Tucker and Dale vs Evil, and Troll 2
I’ve got one that’s the opposite: Tusk (2014) is listed as a comedy, written and directed by Kevin Smith (of Jay and Silent Bob fame), but is actually a horror film.
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.