Testicular cancer is the most common cancer for men between the ages of 15 and 35. That's Deadpool's core audience, so a testicular cancer charity called Ballboys (geddit?) got Ryan Reynolds to don the Deadpool costume and do a few PSAs on how men can check for lumps.
Of course, it's Deadpool, so the instructions are liberally sprinkled with asides about masturbation and the “sexy salad section.”
When you think about it, Deadpool is exactly the right spokesperson for this cause. After all, he does describe himself as a “testicle with teeth.”