So, I tracked down a copy of the second part to the comic where Superman beats up the Legion, in which Superman takes some time out of his busy schedule to fight himself as a teenager:
Admittedly, his own boyhood self is the one to actually pick the fight, so there you go. I'm not even sure that I can explain, coherently, what's going on in this story without resorting to flow charts, but it's fun and a bit goofy.
Keep in mind that Superman's got a history of Self-abuse and Inner Child Issues:
