I recall this actor from the sitcom Roseanne. However, since I'm aware that people may under or overestimate size, as has happened to actor Jude Law or Ewan McGregor, I'm not sure about the accuracy of anyone's descriptions:
Roseanne's Johnny Galecki goes Full Frontal.
Roseanne's Johnny Galecki Goes Full Frontal.
Playwright Douglas Carter Beane on the HX website:
Q: The play includes a nude scene between Galecki and Huff [Neal Huff, from "Let it Out"], which shows off the former’s ample endowment. Were you surprised?
A: You don’t see Neal ’cause he has his back to the audience, but no shortcomings there either! [Laughs.] There was a golden moment the first time it was staged. You saw both of their penises, which are tremendously large, and Julie [co-star Julie White] walks in on them. They cut, and Julie turned and - in all seriousness - said, “Are my earrings reflecting too much?” There was silence. Finally, I just said, “Julie, the odds of anyone looking at your ears this moment are very, very slight.”
From the GLT wesbite: "This young kid (now 29) we grew up with on TV is now fully grown. No, he’s huge! I saw it with my own delicate eyes; when he stripped down on stage I almost went into cardiac arrest."
From some random blog: "Johnny goes full frontal. And may I say, the boy is in fine shape, and VERY well-equipped."
From another random blog: "You may have read by now that Johnny Galecki (who played David on TV's "Rosanne") has a nude scene in the new play The Little Dog Laughed, and that audiences have been wowed by his impressive ... range. I'm here to tell you that there are many reasons to go see this sizzling show at Second Stage Theater, and that Johnny's big dog is only part of the attraction."