Add a word. Ruin a movie.

[claws]

Kindergarten Cop Out
Boogie Board Nights
Frozen Yogurt
This Is 40 oz

[Allhallowsday]

NOT NOW VOYAGER
GONE WITH THE ASS WIND
BAD DAY AT BLACK ROCK CONCERT
THE SOUND OF FART MUSIC  
THE LORDS OF FLATBUSH PANTIES  

[Mr. DS]

Three Men And A Baby Gerbil
Three Men And A Little Lady Lovin'
Glory Hole
Terminator 2: Poor Judgement Day
Twelve Angry & Horny Men

[Mr. DS]

The Lost Baker Boys
IT Burns
True Romance Novels
Orange Pulp Fiction
Children Of The Corn Hole

[Gst0395]

Illegal Alien Vs. Sexual Predator
Porn Star Wars
Fight Bondage Club
Sex Toy Story
A Bug's Sex Life
Up Yours
Requiem for a Wet Dream
Sex Life of Brian
Raging Bull Fight
Mr. Smith Goes to Washington State
12 Years a Sex Slave

I know I'm pretty bad at this, and apologies if I unknowingly copied someone else's. Some of this will probably pass for porn titles more than anything.

[retrorussell]

Horror Express Lane
Eight Men Coming Out
The Devil's Food Rejects

[Rev. Powell]

You can also ruin movie's just by transposing letters:

SANTA WAS A LADY
SANTA'S SADISTS
SANTA'S SLAVES
THE BLOOD ON SANTA'S CLAW

etc.

[Mr. DS]

The BEE Sting
DIRTY Dances With Wolves
Saturday Night HAY Fever

[Mr. DS]

The DISNEY Land That Time Forgot
The Money SHOT Pit
The Song Of The South DAKOTANS
A Christmas HORROR Story
Raw FISH Deal

[Mr. DS]

Pretty In Pink Eye

[Rev. Powell]

If I'm allowed to cheat using hyphens then I suggest

COURT-APPOINTED GUARDIANS OF THE GALAXY

which just sounds more "ruined" to me than LEGAL GUARDIANS OF THE GALAXY.

[Couchtr26]

Conan the Rectal Destroyer
Red Dawn of the Dead (because even communist should be concerned in the '70s)
What about Bob Newhart
Once Upon a Time in the West End

[JaseSF]

Raw Fish Deal
Men in Black Underwear
Revenge of the Nerds Candy
Young Hip Frankenstein
Drunk Cowboys & Aliens

[RCMerchant]

ATTACK of the GIANT NUT CRAB MONSTERS
OCTOp***y FARTS
THERE WILL BE MENSTRUAL BLOOD
LAST OUT HOUSE ON THE LEFT
BLUE BALLS LAGOON
VALLEY OF THE BLOW UP SEX DOLLS

[RCMerchant]

SEX TOY STORY
MARTIN LAWRENCE OF ARABIA
ABBOTT AND COSTELLO MEET THE FOCKERS (ok-thats 3 words...)