One of the *best* comedy fics out there, period.
48 Hours Without a Superman, by Kathryn Ann Kent. Read her other stuff, too!
Here's an oldie but goodie, like just about all of this author's fics:
"Some sort of accident sent your Superman into my future, and sent me backward into his past."
Lois shrugged, "I think I understand, Superman, but aren't you still him...the one from the past?"
Clark sighed, "I guess, in a way, but I need to get back to the time I belong in. I've lived this part of my life already, Lois."
"I can understand that, Superman, but even if you have to relive the past, what difference could--"
"I'm married in the future, Lois. I want to get back to my wife."
Lois could not have looked more stunned even if the sky had suddenly begun to rain goldfish, "I see...that would make a big difference."
Clark sighed and touched her cheek, "I'm married to you, Lois."
This was clearly a bit more than Lois could completely take in. She began to cry and buried her face in his chest. Clark held her and began to stroke her hair, "I know this is pretty overwhelming, and I'm sorry to tell you everything so bluntly, but I want to get home."
Lois sniffed and pulled away. She ran her fingers beneath her eyes attempting not to smear her make-up. Her hands trembled. "If for some reason you can't get back home, Superman, I want you to know I love you, and I guess I always have. We can still...be married." She looked up at him, "I know it won't be exactly the same as before--"
Clark lowered his head. "The hardest part of this is something I still haven't told you, Lois, and though it didn't happen this way in the past, I'm afraid I'm forced by circumstances to do it this way." He rose from the sofa, shrugged and in a moment had transformed into Clark Kent.
