A while back I heard about a blooper reel on one of the Nip/Tick DVDs in which Julian McMahon wore a diaper to prank his co-star Dylan Walsh (who co-incidentally wore a diaper in one of the actual episodes). It caught my attention becauuse I've always found him quite sexy. I couldn't find the clip at the time, and wasn't going to buy the DVD just for that since I'm not a big fan of the show. However, I recently found the clip as part of a McMahon fan video on YouTube. It's very brief, but you can see it. The diaper is actually thicker than I expected, I'm quite impressed.
The diaper part starts around the 0.55 mark.