About to sneeze, he flies up and away from Earth as fast as he can, then, "far, far out into the cosmos," in a distant solar system, Superman sneezes, and his sneeze destroys the entire solar system -- to the extent that each and every planet is blown to bits!
Having just re-read that story a couple of days ago, I thought that scene was just about the funniest in
Showcase Presents: Superman Volume 2.
I guess you could explain the extra destructiveness of Superman's sneeze as being accentuated by the magical cause.
I would be interested to see a survey of Superman's more impressive, if not downright impossible feats, like the time he was towing a solar system or planet on a chain.
I still think the most ridiculously impossible feat Superman performed was in a Golden Age story (in one of the archives - which one I can't remember), where he carried out a number of duties all over the world, all in the space of less than a second, if I recall correctly.