Reign of the Supermen #558: Edible Underpants Superboy
Source: Superboy vol.1 #16 (1951) Type: The real deal (since retconned)
Being the grand finale of "The Strange Costumes of Superboy". Even as he discusses his wonderful line of superhero wear with Highlight Magazine, Superboy is wearing the strangest costume of all! It all started that morning, when pesky Lana Lang intercepted Superboy while he was heading for the mag's offices.
Why are YOU playing hooky then, Lana? She may not be in school, but Superboy is more than willing to teach her a lesson. Also, note Lana's famous last words. So after the magazine interview...
It's Clark Kent dressed as Superboy, talking to his Ma and everything. Caught red-caped! And he doesn't deny he's Clark Kent, and says Superboy is still at the magazine; she can call if she likes. In other words, this comic is perfectly fine with showing Clark and Superboy are exact look-alikes (hardly worth the effort to wear glasses then), and that Clark is just as ripped as his Kryptonian duplicate. Make the call, Lana.
More trolling from the Boy of Steel, who can apparently interrupt phone calls with X-ray vision now. (What do I know about radiation, right?) So why is Clark wearing Superboy's costume? Well he's not, really. That's a special spun-candy facsimile Superboy told him to wear so he could call Lana on her bet. And surprise, it's scrumptious!
Well, at least Clark wasn't naked under there. It could have been a lot grosser.