Ive never had more than 2 in one sitting and never more than 1 without viagra (heck its fun even at 22
) It just hurts too much, you lot must all be freaks!
However i do recall when i was naught but a spotty teenager jacking off to a sears lingere catalogue that after about 3-4 orgasms i would get a sharp cramping pain in my brass (which as you all know is the bit between your balls and your ass).
Biologically my only explaination for this is that the contractile muscles around the vans deferens (the part of your reproductive tract where semen mixed with sperm is collected ready to be fired, the barrel if you will) can cramp as they are not designed as an active repetetive muscle, especially not in humans. They have a slow recovery rate and limited blood supply.
Like the rest of your muscles however they can be trained through use and this is how male porn stars go all day on a few viagra.
Moral of the story, have more sex. But i dont believe there is any evidence anywhere that states you can break yourself with too much sex, go get em tiger!