Have had laundry pins (wood and plastic) and clamps (no the clover's one thou).
Same as when you put them on your nipples, they all hurt when they go on, but the longer you keep them on, the more they hurt when you take them off.
What happens to me personally is that, after I get used to the bite, they are actually easier to stand than the ones on the nipples. But from time to time they shoot waves of pain through my body. And when they come off ... it is stars seeing time!
I'm not sure how long they stayed on the longest, but I'd say more than 10 minutes.
The very first time I had a very strange and interesting reaction, due to mixing the clamped pussy lips with sucking on a cock, an activity that makes me able to stand much more pain. Something clicked in my head and I totally forgot about the clamps but also at the same time I had to actively remember to breath otherwise I would not. It was a weird feeling, as if my body forgot how to do things and my brain had to send active instructions. It was so weird that even Hubby forgot about the pins, until I got back to normal and it was a sudden "FUCK IT HURTS! TAKE THEM OFF!!!" and boy did it hurt even more as soon as they came off. lol.
Clothespins don't bother me. I can barely feel them, honestly. Alligator and clover clamps for nipples are better for me. Piercing forceps down there are hell, particularly on the clit. Makes me see stars. But the bruising is great for later....
Have had wooden clothes pegs placed all over my balls, and along the full length of my cock before, at a party as a bit of a drunken dare, have to say it made me hard as stone and well worth putting up with the slight pain as i got to return the favour to the girl that pegged me!
She seemed to suffer more while removing them from her pussy lips than when i put them on, I did kiss her all better though
So..somebody has some pictures of that party, somewhere, but not me i'm afraid! but i would highly reccomend it