My wife and I have had several, but the other night was memorable. Without being too graphic, let’s just say that my wife is Foreplay for Hours, while I am Limited Attention Span. So by the time she was ready I was not. So I apologized by saying “it’s time to advance to the front, and I’ve got a deserter. The coward”. My wife thought this so hysterically funny she was ROTFL. But eventually everything worked out.
I suppose you didn’t video it?
Losing my class ring in her…ah…uh…yeah, while manually, ah, stimulating her. In a graveyard at 2am no less. Nope, sorry, no videos here either.
When I was in high school, I was making out hot and heavy with my boyfriend, and I started to taste this strange, salty taste and felt this wet feeling on my face, and I thought I had a runny nose, but it turned out I had a bloody nose and it was all over our faces! Let’s just say we didn’t go all the way that night, but it was pretty funny (and a little embarassing, and in hindsight kind of gross, but funny nonetheless!)
Cats…
That’s all I’m gonna say.
Ever gotten a cold, wet, dog nose poked in your butt during times of intamacy? No? Good.
I was due to fly out to California in a few weeks to see the Love of My Life to see if the old magic was still there. As we were talking, he started laughing out loud at an add he’d seen in a wargaming magazine which had the headline, “Thrust home your wad!” Those who know me well can tell you I have a streak of sheer raw evil in me. Sure enough, a few weeks later, when I arrived in California, the old magic was still there and we were enjoying things to their fullest. Just as things reached their peak, I had to do it. I had just enough presence of mind to gasp out, “Oh ____, thrust home your wad!” 
I heartily recommend laughing and coming at the same time.
I also tip my hat to an Atheist friend of mine, who, under similar circumstance, managed to cry, “Oh random! Oh chance!” I heard it from the gentleman she was with who agrees with me about laughing and coming.
WonTon Sean, forget video – I want audio of that moment!
CJ
Forgot to wash my hands between chopping chillis and advancing to, errrrm, ‘other activities’ - she ended up dashing to the shower and spent ten mintues rinsing with cold water.
My gf and I were making love late at night, about 11:00pm. Just as I reached climax, her clock starting chiming 11 loud rings as I was in the middle, then finishing. Just as I reached the end, the chimes were still ringing, I started to laugh my head off. Felt like I was being timed and had to beat the clock.
Knocking boots in an antique four poster bed in a bed-and-breakfast, and having the slats fall out…
Actually, the funniest moment in the sack involved not doing it. Less than a year after the piratess and I were married, we got a cabin with her whole family. We had our own room, with the rest of the family scattered through the rest of the rather small cabin.
So we get into bed and it is an ancient bed with rusted springs. As she gets in, there is a loud SQEEEEEEEK which we knew that the rest of the cabin could hear. Well, this starts her off in a fit of giggling, which starts the bed going sqeeeka-squeeka-squeeka. Of course, this sets of a further fit of even more intense giggling squeekasqueekasqueekasqueekasqueeka. This just feeds on itself more and more. Soon she starts gasping for breath since she simply cannot stop laughing, and her laughing tends to sound more like squeals and screams. Finally she manages to get herself under control.
We got some strange looks at breakfast the next morning.
The funniest and most painful. We had a bed that had a headboard that was about a foot deep, had doors on the front and was typically used for storage. On top of that headboard was a radio. You know what happens to radio’s that are on headboards during sex? They fall down on your face, nearly breaking your nose. After seeing stars and from what I’m told, clenching a lot, we both burst out laughing.
Funny embarassing. We lived on the second floor of a small apartment building, think a big house with 5 apartments. There was a bar on the next block. One hot, sweaty summer night we were going at it with the windows open and when we finished, we heard a loud, rousing round of applause, complete with cheering.
ROTFLMAO*
I suppose one of our funniest was one night when DH and I were still dating and we were going at it in the front seat of his ancient Pontiac convertible outside a Little League baseball field. There wasn’t a game that night and it was nice and quiet so we figured we’d steam up the windows a bit. After about an hour or so, we noticed a bright light shining RIGHT AT US. Somebody had called the cops and there was an officer shining his flashlight directly into the car staring at us with this very menacing glare on his face. Needless to say, we got ourselves arranged sufficently for us to get the heck outta there.
We did laugh about it later though…how we got busted by some member of the Morality Police. 
CartoonSu
There was an extremely close call when I was in college that we thought was pretty damned hilarious after it was over. Keep in mind that this was at a very conservative university where unwed intimacy was heavily frowned upon by the administration. And that my roommate at the time was a horrible gossip.
My roommate had good home for the weekend (his parents lived across town), so my GF and I thought we had my dorm room all to ourselves. Part of our foreplay involved my undressing her one garment at a time in preparation for a leisurely sponge bath. Just as her last garment hit the floor (I was still fully clothed), we heard my roommate’s distinctive voice talking to someone right outside the door. My GF, completely in the buff, jumped onto my bed and threw the sheet over herself. No good. Too obvious. I grabbed my basket of clean laundry and dumped it on top of her. Just as the door started to open, I remembered to kick her clothes under the bed.
The ensuing scene was like something out of movie. Roommate comes in and says he came back to pick up a textbook he’d forgotten, and is now thinking that he doesn’t want to drive all the way back. He actually sits on my bed, inches from my GF, picks up a couple of socks from the pile (aren’t these mine?), and starts looking through the pile for any more of his clothes that ended up on the wrong side of the room. I said something (I don’t know what) to try and distract him, and he turned to look at me. Had he turned back around at that moment, he would have noticed that he’d just uncovered one of GF’s (rather spectacular) breasts. I watched in agony as her hand come slowly out from beneath the clothes and covered herself from further view. I don’t know how it was humanly possible, but the roommate never noticed. I could smell GF’s perfume from across the room and actually hear her breathing.
Finally, after what seemed like an hour (but was probably only five minutes, the roommate stood up, gathered his books, and left.
Once the terror of near-discovery had passed, we laughed until we cried.
Kizarvexius, how do I send you my ER bill? Laughing so hard I hurt something! (Snicker, giggle, snort)
back in time*
I’m parked way out on a suposedly little used road… the lady friend and I are just starting to get going. Oh yeah.
I look up and through the back window… is that a car?
FWASH
I am blinded as the nice police officer hits his hi-beams. Hurridly throw clothes on and jump out of the car.
the funny part was explaining to the cop that the lady in the car (whose busily putting her pants on inside out… apparently it’s hard to get your ID out of your pants with them on that way) is a good friend of my wife and I’s.
To much fun.
You asked for TMI…
Once
You asked for TMI…
Once I was performing oral sex on my ex-wife. As she reached climax, moaning and grunting, she, quite involuntarily, let loose a big ole fart… right in my face…
She thought it was quite hilarious. I thought it was less so…
You may also enjoy Whammo’s “Funny things said during love making/intimate moments” from a few years back. (Daymn, now I feel all old!)
Sorry to say I have nothing to add since then, but you’ll love “are you the sheriff?” and “was that a leg?!?”
http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=24960&highlight=lovemaking
Best. Thread. Ever.