“The Hump of the SpermBack Whale”
Oh, there’s so many.
There are the inside joke style, such as my girlfriend and I enjoy. We’ll take regular movie titles, and then pornoize them, and then one of us will ask the other if they want to go home and watch that flick. It’s sort of a under-the-table way to say “Let’s go home and screw”.
For example, I’ll say something like “Wanna go home and watch Crouching Beaver, Hidden Ferret?” or “Let’s go home and watch Free My Willy.”
It’s lots of fun.
Another favorite is “bumping uglies” or “nookie”. And let’s not forget “Make Whoopie”. Heh heh, that one always makes me laugh.
Chef from South Park refers to it as “Sweet, sweet lovin’” and I like that, too.
Other times, I’ll be hanging out with my brother and we’ll see a hottie and say
“Man, I would stick it in and break it off!”
or
“Bag that up, I’m taking it home.”
I guess these are more euphemisms for attractiveness, but hey, I think the two are mutually interdependant, you know?
Other euphemisms for sex are:
Wease some love juice
Do the hibbedy-dibbedy
Work the love-muscles
Makin’ bacon
Play hide the salami
Get your pole varnished
Buff the wood
Shine the helmet
Get some booty
Churnin’ some butter
Pop your rocks
Pop your cookies
Get your rocks off
Get off
Get down
Clean her pipes
Wrestle the anaconda
Abuse
Molest
Rock your world
Ride the hobby horse
Kick the kitty
Shag
Screw
Make love (this is my favorite because it sounds so ridiculous)
Make a deposit
Make a donation
Drop a load
Ravish
GrizzWife and I use “making cookies” and “going to Toledo” as euphemisms.
yes, I know, they’re not racy. But it lets us talk about sex right in front of the pastor’s family without a blush!
The beast with two backs is my fave.
How about a little Strine’? As in;
“Playing cars and garages.”
and
“Playing hide the sausage.”
Aw crap! How could I forget “Park the Pink Cadillac”?
My friend Jeremy refers to it as “getting his nut on”. He also refers to eating as “getting his grub on” and studying as “getting his learn on”. He’s also spent the past three years at a two year technical school.
“Changing the sheets.” Inside joke. If anyone is brave enough to ask, I’ll tell you. 
Ex and I called it “Bouncy Time”
That’s always been my favourite.
Since the introduction of Poofy to the boards, “making pig bacon” has got to be one of my favorites.
Also, “throwin’ a hump” as in “I threw her my best hump and she still wasn’t satisfied!”
I like ‘bumping uglies’.
So, did you tax that ass?
or did you hit it?
Steps Up To The Plate
I’ll assume it has something to do with unintentionally removing them whilst in the act - Or marring them so badly you needed new ones. But then again - who asked me.
Like Brynda said, the “boots” in “knockin’ boots” are boots. It’s also “knockin’ sneakers” (just not as often). Ten toes up and ten toes down and you didn’t take the time to get your boots off. Yeah, they’d knock. If you’re “knockin’ booties”, either you’re real bendy, or you just aren’t doin’ it right.
Also a bit of the classic: Nookie.
Bumpin’ bellies
I have got to loose weight:(
Making love.
Whilst never in reference to the caring, sensitive relationship between the woollies
Bendy up Wendy
Percy wearing his pink anorak
When I lived with my parents, I would bring my girlfriend home and we would immediately head for my bedroom. My family would accuse us of “scampering”. And if a friend would call me while we were busy, my mom would tell him that I was “entertaining” my girlfriend.
My two favorite generic expressions are “laying pipe” and “the old in-out”.
Sometimes the classics are best, and in my and my SO’s case we both like to “fuck.” That’s when its sweaty, powerful, full bore, take no prisoners, scorch the sheets fun.
Yes “…umm” can often add suggestiveness to any phrase. In fact, we found that it does it so well that, rather than go through the effort to come up with a euphemism, we’ve just resorted to saying ‘um’ by itself.
“You gonna feel like umm tonight?” or “You wanna umm?”
We’re figgering that might hold up well once the cubette gets older.
…and “Bumpin’ uglies” always cracks me up.
On a related note, I’ve also heard it called “mashin’ nasties.”