I have a whole collection of kidish briefs that I like to wear when i'm not wearing diapers. I wish there were more variety other than comic but, it's still kid-ish. They're all in adult sizes.
I have the following designs and prints:
(from ebay, user kristieskids)
prehistoric dinosaur with baby blue trim
baby bugs and spider print with royal blue trim
(From walmart, also seen on amazon)
Superman with black trim
Batman with blue trim
anime comic strip, more a boxer brief style
(Also from walmart, but with awkward fit, works well over diapers, also seen on amazon)
Spiderman, royal blue trim
Ironman, red trim
misc comic strip from DC-comics, white trim
Misc DC characters, black trim
being a big kid is fun.