Journalistic etiquette decrees that any delicate questions are usually saved until near the end of an interview. That doesn’t apply, however, when you are talking to a man who has written a standup show about his penis – or, rather, the piece of it that was stolen from him as a baby. Tom Rosenthal, the 31-year-old star of the sitcoms Friday Night Dinner (about the embarrassments of a Jewish family) and Plebs (anachronisms and dick jokes in ancient Rome), meets me at his agent’s office and cuts to the chase. “Ever since I became aware of what had happened to me, I’ve never felt so sure that something is wrong.” The earnest tone signals that any jokes on the subject will be confined to the stage. “I just don’t think it’s very funny.”

Fortunately, the show is. Manhood traces Rosenthal’s gradual realisation that he didn’t want to belong to a club that would have a member like his as a member. First, there was the “little sleeve” he noticed on a classmate’s penis. Then came the terrifying circumcision video shown at his school when he was 12, which led to a confrontation at home. “I had a shouting match with my mother. She took me to a doctor who basically invalidated all my feelings. The truth is that my parents were put in charge of my welfare and they did something to me that can never be remedied.”

This is all some way from Richard Herring’s hit show Talking Cock, which scrutinised attitudes towards male genitalia but kept the knob gags coming. Although Rosenthal’s set is hilarious, it is also candid, angry and often painful. An earlier version was “a bit too much like a Ted Talk”, with the balance tipped in favour of some formidable and wide-ranging research. Only once he started emphasising that he had skin in the game, so to speak, as well as interrogating the justifications for circumcision, did he locate the show’s real power.

Nothing is off limits in Manhood, whether it is the adverse effect circumcision has had on Rosenthal’s sexual performance or its relationship to his OCD. The details extend even to a discussion of his father’s genitalia. Yes, that is the penis of Jim Rosenthal, the sports presenter named by the creators of Alan Partridge as an inspiration for their gauche and gaffe-prone Norfolk-based broadcaster. Rosenthal Jr has already mined that area in his 2011 fringe debut, Child of Privilege, where he discussed his father’s failed attempt to sue Heston Blumenthal over a food poisoning incident.

“My dad liked the idea that I was taking the piss out of him,” he says. “Of course, discussing his penis is slightly more intimate.” One of the reasons Rosenthal was given for his own circumcision was that “a boy’s penis should look like his father’s”. I had assumed Rosenthal Sr was circumcised for religious reasons, but his son, who has got a lot of comic mileage out of being mistaken for a Jew, sets me straight. “The last proper Jew in our family was four generations back. My dad was circumcised for medical reasons, which is another bloody rabbit hole because a lot of those cases are misdiagnosed.”

What is his father’s attitude to the subject now? “He’s very funny. And not in the way I’d like him to be. He’ll say: ‘Doesn’t sex feel good? My penis is fine!’ He cares about the fact that I care. But he doesn’t care for the reasons that I care about it.” Rosenthal’s parents will see the show in Edinburgh. “Dad said initially that he wouldn’t. He thought it was a revenge show, a ‘fuck you’, and it isn’t that at all.”

When I ask whether he can forgive his parents, he spits out a mirthless “Ha!” then furrows his brow. “That’s a really hard question. I think they asked me this. I’d forgive them everything. I’m thankful they’ve been so open to me.” He is aware that as a white, middle-class, heterosexual man, he doesn’t have a lot to complain about. The fact that his circumcision is the defining horror of his life is, he points out, “an indication of how nice the rest of it has been. But it’s one of the fundamental sadnesses of the whole thing, and one I hope to get past, that whenever you have sexual interactions, it’s on your mind. Which obviously isn’t optimum.” It even affects his choice of porn: “I prefer to watch uncircumcised penises because I like to see how they work.”

The last thing he wants, though, is to make men who are contented with their own equipment feel damaged or defensive. “The aim is to recognise that if this has happened to you and you feel fine about it, that’s great. But if you don’t feel fine, which I don’t, then you’re justified.” It would be nice also if the audience laughs. “Yeah! Someone obsessed with their dick should be funny, regardless of the cultural ramifications.”

Manhood is at Edinburgh Pleasance Two until 25 August, then touring