Source: Superman's Pal, Jimmy Olsen #41 (1959) Type: Transformation or hallucination
So this one starts after Superman drops some alien artifacts at Jimmy's so he can write articles about them and add them to his collection. These include a glowing meteorite (uh-oh) and an alien space fruit that Jimmy accidentally takes a bit out of.
I guess it tastes just like pear, and since the people who eat it have six arms, well, who knows what it could do to Jimmy? I mean, it has the exact enzymes required to stimulate one's cells so they specifically grow extra upper limbs! Science! Jimmy laughs it off, but adds to his reserve of nightmare fuel by watching a documentary on the noble octopus that night. So obviously, when he wakes up the next day, he's got 6 arms. But Jimmy doesn't think that's necessarily a bad thing.
Push-ups are easy, for example! (Yes, that means you won't be getting more muscly, Jimbo.) But Superman is down on the idea. He calls it a handicap and won't let Jimmy enjoy the moment. It's almost like the Man of Steel can't stand to have another person with unique abilities in Metropolis (hey, this is the guy who forced his Kryptonian cousin to hide in an orphanage). But you can't kill Jimmy's buzz!
It's not just extra arms, that's some rather improved coordination too! After a quick stop to the tailor to add some sleeves, Jimmy is back at the office writing three articles simultaneously!
How is his brain WORKING? Well, doesn't matter because Perry can't keep him on the payroll without paying him three times the salary. Union rules. He's costing people jobs. But who cares, right? Jimmy can make his money doing other things, like fight in amateur fights. He just needs to make sure he hasn't changed weight classes with his extra limbs. Aw, crud!
For his next trick, Jimmy signals a turn with all his arms and causes an accident. People aren't ready for his multi-armed awesomeness. He does pretty well with the games on a fairground, if only he could pay the rent with stuffed animals, but finds Lucy isn't quite as imaginative as he would like her to be.
Then some crooks force him to become a super-pickpocket, which is an astoundingly stupid plan. It's not like Jimmy suddenly knows how to pick pockets!
So he gets arrested for his trouble, and Superman bails him out so he can gloat, oh and also find a cure for his condition. A million experiments later, Jimmy drinks the antidote and both he and his suit are back to normal. Wait, his suit?! Yes, because Superman reveals the space fruit sometimes causes hallucinations, so maybe he just imagined the arms. And apparently, the whole adventure. Except the bit where Superman tries to find an antidote. Uhm... And no one remembers anything from that day so... Why can *I* still remember the story? Nothing about this is fair.