Jason Russell + Kony 2012_TMZ has footage of "Kony 2012" honcho Jason Russell in the midst of his naked meltdown in San Diego ... pounding his fists in anger and screaming maniacally.

As we previously reported, Russell was detained by police yesterday ... after witnesses say he was running around naked and making sexual gestures.

Russell was held on a 5150 psychiatric hold ... so authorities can decide if he poses a danger to himself or others.

A rep for Invisible Children says Russell was suffering from exhaustion, dehydration, and malnutrition as a result of a strenuous PR campaign.