List your fave movies that where supposed to be serious but something went wrong in the process and the result is a comedy gold.
Mine are [in no particular order]:
Burial Ground
Hell of the Living Dead
Flesh for Frankenstein
Death Wish 3
Invasion USA
Ice Cream Man
Plan 9 from Outer Space
I thought The Green Berets was quite funny
Check out Hostage Hotel with an over the hill Burt Reynolds, the guy from Sledgehammer trying to act in a serious manner and Jefferson from Married… With Children as a tough guy federal agent.
The film itself is a cross between Rambo and Home Alone. "Fugazi, baby!"
From the film:
[KABOOM!]
“What was that? An explosion?”
The Remake of WICKER MAN with Nicolas Cage! 
A lot of 80’s Action Movies with easy exploding cars are good comedies.
Death Wish 3, Road House, Invasion USA, …
The Blair Witch Project
The Punisher (2004) - gotta love Travolta being over the top - nothing makes sense in it.
Scarface
How about Watchmen? One of the sillies things i´ve ever seen…
Is it similar to the graphic novel? If it is it can’t be bad
it’s very similar to the GN and no it’s not silly.
The graphic novel is one of the best things i’ve ever read. Alan Moore is a genius writer.
I remember liking the comic when i was aorund 15, but the film was really, really bad. in a fun way!
I’ve almost forgotten to disagree with The Magnificent Gringo 
I always thought the novel is pretty much unfilmable. Did they simplify it? Or maybe they made a mess out of it?
Well, i guess what looks good and believable written down and drawn in a comic can sound and look really stupid and overblown in a movie, like watching a blue, nude man holding speeches on the evils of mankind while standing on Mars…
to me it was like a funnier Waterworld. But that´s just what i thought…
Haven’t seen it, but I’d say that’s quite a silly idea
Nude men usually are I’m afraid
Refer Madness
“Heck Comes Home”, a really shockingly awful boy-and-his-dog TV movie made in Canada. There is some unintentional comedy in it, but on the whole, nothing anyone should really have to watch.
Transformers
Like the bit when Harry Dean Stanton is trying to catch a fly in Cisco Pike when in the bathroom and he trips and dies.
I remember laughing hysterically at one of the Nightmare on Elmstreet movies but I forgot which one it was.
Also the Lou Ferrigno Hercules movies.