The 'Knocked Up' actor has been making penis gags since a mohel - someone who performs the Jewish circumcision ritual of Brit milah - hired him when he was a teenager.
Seth, 26, told E!: "My first break was when I did stand up comedy at a lesbian bar for the first time, and it went well."
"Soon after that I was hired by a mohel to write jokes. He saw me perform and he wanted his circumcision ceremonies to be funny. He approached me - I was 15 years old - and he said to me, 'I'll pay you $50 an hour to write circumcision jokes for me.' So, I did it. See - I've been writing d**k jokes since day one. That's sad - I just realised that."
The Canadian-born star continued to perform stand up routines and won the Vancouver Amateur Comedy Contest aged just 16.
Seth recently admitted his personality and humour haven't proved as popular with children.
He said: "I did a meet-and-greet with kids after a premiere in Australia. I realised kids just don't like Seth Rogen. I scare the s**t out of them. Maybe it's my laugh or that I'm a big, hairy guy. They just don't like me."
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