Here's one that might get interesting. Direct him to this webpage:
Faithfreedom Challenge
It's a page by a former muslim. On this page he challenges muslims to disprove his assertions that(direct exceprt from the webpage):
I accuse Muhammad of being:
a rapist
a pedophile (had sex with a child)
an assassin
a mass murderer
a ruthless torturer
a terrorist (I have been made victorious through terror)
a lecher
a misogynist
a narcissist
a thief and plunderer
a cult leader
a mentally deranged (was paranoid, heard voices, hallucinated of seeing jinns, Satan and angels, used to think he had sex with his wives when he did not, suffered from depression and had suicidal tendencies).
If he can successfully challenge the author, the prize is $50,000 USD.