I've heard of the rare "rigid dick snaps like a stick" type mishap. Chuck Negron of Three Dod Night had the same type of injury:

http://www.spinner.com/2008/05/09/twisted-tales-three-dog-night-singer-suffers-groupie-related-gr/

A more common sex injury for uncircumcised men is the dreaded "split foreskin".
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