SimCity 2000 (and many Maxis spinoffs) show the phrase "Reticulating splines" on the loading screen, which was probably not the first funny loading message, but the first one I think of. https://unsung.aresluna.org/some-rather-obscure-and-complex-mathematical-process/

Reticulating splines is always my go to, as I think everyone else here has mentioned! 🤣

Earliest I can recall is Sim City 2000, but spoofing overly-serious progress bar info probably didn't start there...

I first noticed the trend in video games. Perhaps that would explain the irreverent nature of the messages.

That being said, most progress bars are just theater. If you want to have a good laugh, do a phone number search and hit one of the thousands of gateway pages for paid lookup companies. They will literally sit you through 10-15 fake progress bars before dropping you to a payment page.

Sim City is the first I can remember

I agree with others that SimCity 2000 was one of the earliest, if not first. So many things now just have a spinner to pretend things are happening without any sort of calculation or commitment.

Not sure where it started, but the earliest that comes to mind for me is "Reticulating Splines" from Sim City 2000.

World of Goo, released in 2008, had a series of goofy progress messages like that. I don't know if it was the first, but it was the first one that I noticed.