I know you said no characters, but what about Thomas the Tank Engine? I don't like cahracter undies either, but these were the only ones I got that were characters that helped in the beginning of pt. (got them at walmart) Now ds wears boxer breifs, they just seem more comfortable
Kohl's had some a few weeks ago. We got dinosaurs, but they had cars, trucks and tanks. They were pretty pricey $15 for 7, but I got the during a 50% off sale. They have them often, so watch the ads. Also I think Hanes makes some with Matchbox cars on them, so half way to what you are looking for.
I'll have to check Kohl's. And Matchbox cars would be fine too.
We do have 6 pair of Thomas ones and they are Noah's faves!! We just have to change somewhat often and I was looking for some variety. Every store we go into has all these characters he's never even heard of- Sponge Bob, Scooby-Doo, Rescue Heroes.
Where did you find the boxer briefs? I think Noah would like those because that's what his daddy wears.