The basic idea of this dare is that you get to tie each other up in such a way that you both get to have fun and still get to have sex.
Firstly the Girl:
1. Attach nipple clamps or pegs to your nipples. Make sure that you have the ability to attach string or rope to them. If you have clamps with a chain all the better.
2. Tie around the base of each boob until they are nice and tight. I find the easiest way to do this is to have my partner on all fours but that's up to you. The idea here is that the nipple clamps go on first and when the boobs are tied the skin is pulled tighter thus making the clamps more effective.
Now the Guy:
Get some string and tie around your balls and the base of your cock. Get them as tight as you can handle. Make sure that you have a reasonable amount of string left because it will be attached to the nipple clamps.
Together:
Once the boobs and balls are tied, get into a doggy style position (I guess missionary would work too) and get as deep into her pussy as you can. Then (this will require some flexibility) you need to attach the string that is hanging from his balls to the chain/string on the nipple clamps. Make sure that it is taught so that when he pulls out it pulls on both the nipples and the balls at the same time. The gentler you are in your love making the less the sensation, the rougher you are, the more pain you get to enhance the pleasure.
Let us know how you go.