Adam Devine has starred in lots of movies and tv shows about hapless dudebros who have their cock or butt put on display as a form of humiliation, but Tony Cavalero didn't have many starring roles before Keefe, so no humiliation nudity. All I found from his pre-Gemstone work was Ozzy Osbourne sticking a dollar bill up his butt in The Dirt, and this photo from Tony's instagram, nude with a cat sculpture covering his privates.
The Righteous Gemstones has given us a bit more. In Season 2, Keefe appears in a jockstrap several times, notably as he is preparing to try the cross-raising challenge.
Keefe does some splits on the ground to warm up the crowd, and coincidentally to present himself as an erotic object. Oddly, he appears to be a bottom. In Season 3, he is totally a top.
Other than the single testicle and the mushroom head, the only cock shot comes in Episode 1.9, when Keefe is immersed in an isolation tank at Club Sinister, and "regressing to a transitive state."
Why is his cock exposed? Why is he aroused? Some viewers speculated that it is for the pleasure of the partygoers, but they'd have to splash through a milky liquid to get to it. Maybe just for its aesthetic appeal.
Cavalero said in an interview that the cock was "mostly" him. You can't stay aroused during an entire lengthy take without a fluffer, so they would need a prosthetic for the arousal.
But where does the prosthetic end and Tony begin?
I guess you'll have to ask someone who has seen him aroused in real life, like his wife Annie, or Adam Devine (long story). Or see if he has any openings for a fluffer.
See also: Keefe's Capacious Cock, Part 2: The Mushroom Head
Tony's Hot/Hung Photos,Part 1: Boner pills, Death Water, dildos, and "Why the hell not?"