How about a few Simpsons “Treehouse of Horror” episodes?
From that time period, exposed boobs would still rate only PG. To get an R for nudity in 1985, it would have had to been full-frontal (or, as we used to say in elementary school: “You can see everything!”). I’m guessing it has an F-bomb, which in 1985 was still, IIRC, an automatic R.
That’s really too bad because it would seem that Slither was tailor-made for your situation, but it is rated R for horror violence and gore. (No nudity that I recall.) And the cast is fantastic, with Nathan Fillion and Elizabeth Banks playing the leads, plus a cameo by Jenna Fischer.
imdb lets you search for PG-13 horror films, btw. Go to this page, scroll down to section 2 and select “Horror” as both genres and then enter “USA:PG-13” (no quotes) as the Rating Certificate. I added in a date filter to include only movies made from 2000-2010, and ended up with a decent enough list. Here are the ones I’ve seen and can say that they held my attention to watch until the closing credits. (I watch a shitload of movies of most genres, including horror.) Cheese factor varies wildly.
1408*
Anacondas: The Hunt For The Blood Orchid
AVP: Alien vs Predator
Boogeyman
The Cave
Cursed
Dark Water
Darkness
Darkness Falls
Disturbia*
Eight Legged Freaks
The Exorcism of Emily Rose
The Fog
The Grudge
The Grudge 2
The Mothman Prophesies
The Others
Pulse
The Ring
The Skeleton Key
Stay Alive
What Lies Beneath
When a Stranger Calls
The Wicker Man
- Haven’t seen it because they are too recent to hit cable, but I want to and I think they’re out on DVD.
Eight Legged Freaks is the clear winner. It’s funny as shit, and features Scarlett Johanssen. Greatest movie ever. If you want scary instead of schlocky, I’d go with The Ring or The Grudge. Note that some of these were released with both a PG-13 and an R-rated version. Be sure to get the PG-13 one if it matters. (If not, get Slither.)
I am happy to discuss the merits of any of the above titles in a group-viewing context if you’re torn between several.
Then how about SSSSSSS? It’s hilarious!
2005-2007 horror movies without gore:
An American Haunting
Blood and Chocolate
Boogeyman
The Covenant
Dark Water *
Dead Silence
Disturbia
The Exorcism of Emily Rose *
Hide and Seek
The Messengers
Monster House *
Premonition
Pulse
The Reaping
Requiem
The Ring Two *
The Skeleton Key
Skinwalkers
Thr3e
When a Stranger Calls
White Noise
The Wicker Man
Other good horror movies without gore:
The Others (2001) *
The Other (1972) *
The Haunting (1963) *
The Innocents *
Night of the Demon *
Ringu *
The Eye *
Rosemary’s Baby *
The Night of the Hunter *
Wait Until Dark *
Poltergeist *
Gremlins *
Pulse *
Tim Burton’s Nightmare Before Christmas *
The Legend of Hell House *
- Recommended.
That’s not the one from Adaptation is it? 
What do you mean by “cheesy”?
Lots of great suggestions. The more serious ones would appeal to me – I love Nosferatu and The Haunting – but I know the crowd (who gets to vote) is going to go for goofy. Pity about Slither. Eight Legged Freaks and Monster Squad have definite possibilities.
Current front runner in the office: Killer Klowns from Outer Space. I’ll let you know what we finally decide.
*The Birds
The Old Dark House
Frankenstein *(Whale)
*I Walked with a Zombie
Leopard Man
Cat People *(Tourneur)
*Dracula *(Browning)
House II
The Mummy & MummyII (Brendan Frasier versions)
Another vote for Tremors. Funny, and worth it just for the scene where the monster breaks into the WRONG rec room.
The Hammer version of The Phantom of the Opera (1962) was actually pretty good if I recall correctly.
Damn youse, DrDeth! House II was going to be my recommendation. It’s excellent, and cheesy - John Ratzenberger shows up for an excellent cameo.
They Live , featuring “Rowdy” Roddy Piper and the world’s most protracted fight scene.
Plus it’s genuinely thought provoking (the movie, not the fight).
How about Arachnophobia?
I’ll add another vote for Tremors.
Just because they found the best lame excuse to get a woman half naked.
I haven’t seen this since I was a child, because it scared the living daylights out of me, Audrey Rose.
I found Killer Klowns from Outer Space to be lame.
How about the original The Blob?
My family just saw this at an Attack of the B Movies event at our local cinema. While calling it a B movie is generous, the title has nothing to do with the plot and the monsters didn’t really display a full range of motion, it was great fun and perfect for watching with a group a la MST3K.
Sounds like you’re going for goofy/cheesy, but I’m going to mention Night of the Hunter anyway. It’s got a kind of dreamlike creepiness, and Robert Mitchum is pretty scary.
I don’t remember an F-bomb. Fright Night actually has a sort of innocence about it. The negligee scene is the only thing I can remember that might have caused the R rating (and I re-watched it recently on cable). The funny thing is that the breasts are very obviously fake and plastic. And even at that, you only saw them vaguely, through sheer fabric. There was also a side-angle shot of male nudity, but no naughty bits visible.
I think you are mistaken about the breasts thing, though. Weren’t breasts an automatic R back in the day? I can’t remember a PG movie from that era with exposed breasts.
There was some gore in the movie. Very minor by today’s standards, though. Maybe that pushed it over the edge. I don’t think the film would get an R if it were released today.
I think you shouldn’t limit your choices with the arbitrary and utterly subjective and fascist MPAA rating system, even if it is an office party.
Children of the Corn is pretty scary and worth some jeers.
In The Mouth of Madness is a surreal cheesefest and will leave you all thinking wtf? Not a lot of people have seen it either.