Took my pants off,saw tons of black stuff sprinkling down from my scrotum.discovered flaky dead skin allover my scrotum.not painful. what can this be?

Old skin: You already answered your question in a way - the black stuff is likely flakey dead skin. Since it is not painful, it is unlikely to be a bacterial infection. If there is itching, it could be secondary to a fungal infection or even chafing due to exercise. "jock itch" is due to a fungus, and often causes darker skin in affected area. It would be best to see your Dr to make a definitive diagnosis

Dermatitis : This dermatitis could very well be from a fungal infection similar to jock itch. It could also be from an allergic reaction to certain chemicals or materials. Pubic lice could be another possibility as well and this can be transmitted via sexual contact. A medical evaluation is warranted and treatment will be based on the finding.