I agree that it's odd to not realize you're not wearing underwear but I appreciate the joke. I commented how glad I was that Bulma didn't realize what Goku had done in chapter 2, in part because her lashing out at him for being a pervert twice in one chapter would've been overbearing, but I did really like how this turned out to be a multi-chapter pay-off. Often times gags like this are self-contained, there's not many comedies that do lengthier gags with a prolonged pay-off chapters after it's set-up. And sure, it's only like two chapters later but still, most manga I've read don't tend to do that, set-up a gag that it goes back to and ultimately delivers the punch-line a few chapters later. That kind of interconnectivity is something I really appreciate.