The first time I saw “co-worker” spelled “cow-orker” (right here on the SDMB), I assumed it was a mere typing error. Then I saw it again. And again.
Are people who spell it that way trying to be cute, or do they really think that’s how it’s spelled?
Or do they all work on dairy farms, and spend their time orking the cows?
Cute. And indirectly labeling them cows.
I believe someone made a typo originally and then, one after another, others thought it looked funny enough to keep using it. 
Manny peoples they try googling it.
Because they find their co-workers to be cows and irkers (say it out loud - it comes out the same)
It’s from Scott Adams and the Dilbert Newsletter. At least, that’s the earliest I ever saw it. It first appeared in Dilbert Newsletter 17.0, August 1997:
I belive it got its start in the Dilbert newsletter (Dogbert’s New Ruling Class). I found an old one with a glossary here, just scroll down a little.
It’s been used on Usenet for longer than that, in newsgroups like talk.bizarre and alt.folklore.urban. A Google Groups search shows the term first becoming common in 1993. In this post from that year, someone claims he’s been using the term since 1989.
I first noticed it in the professional journals I get. These journals spell the word “coworker” which to me (if I didn’t know better) looks like it ought to be pronounced cow-orker. I’ve been getting the journals now for over 10 years.
I suspect the “cute” spelling comes from a lot of other people looking at the unhyphenated word and thinking the same thing I did.
Agreed. I think it’s just a consequence of the trend toward dropping the hyphenation from “co-worker”; the pronunciation suddenly appears ambiguous. Similarly, I always think “shortlist” looks like an expert in shortling.