He talks specifically about that joke on SNL, “I do look back at a joke I made on Saturday Night Live in 2014 and I very much regret making that joke. It was a terrible joke, honestly.”
The joke referenced messages that were made public between Franco and a teenage girl in which the pair apparently arranged to meet up.
The joke was as follows, Rogen pretended to read from a journal entry saying,
“I decided to prank James Franco. I posed as a girl on Instagram, told him I was way young; he seemed unfazed. I have a date to meet him at the Ace Hotel.”