Probably there isn't any, not at least one you can consider it's original source
And I'll try to elaborate a bit with some personal experience on the subject:
Well... being a roleplayer from at least 34 years, my first encounter with this joke was speaking with friends about AD&D (2nd edition).
When we started playing AD&D we spoke a lot about classes, and we concluded that a lvl1 mage could fight a cat (assuming he knows magic missile) but will be in serious trouble fighting two cats. And we assumed that home cats would be lethal to their owners, as a commoner had 1d4 hp AC10 while cats made 1d4 damage and could hit them fair easily.
This was before any homebrew rules (or further companion books) added more resilience to starting characters, giving max hit points at lvl1, adding the possibility to don't die at -1 hit points, etc...
The fact is that this joke was something widely shared with lots of people at conventions and events during the time. I don't recall reading it anywhere, but everyone just had seem to reach the same conclusion as we did: cats are mean and dangerous (at least it were with the standard stats of the game).
I don't think this "joke" started in any particular article or publication, I think this is one of those things that was quite obvious to anyone who started playing the game, and naturally became a trope that moved mouth to mouth until reaching legendary proportions.
I will add a bit further on my answer based on comments.
First of all, I cannot prove that something that doesn't exist, in fact, doesn't exist. But I think that my answer goes further than the experience of a single person. During the years, and mainly during the first years after the game was just published, I shared this joke with a lot of different people in a lot of different places. Never hear anybody speaking about having readed it on any written source nor had readed myself anywhere.
Keep in mind that around early 90s there weren't so many publications and sources, and the few that existed took quite a while to reach remote places, there weren't anything remotely near than you can have today and knowledge in this hobby (which by the way, by that time were also far more underground that nowadays) moved much much slowlier than today. However, a lot of people from different places and backgrounds shared this joke from different angles and perspectives almost from the very beginning of the game.
It's far more probable that this joke were something that emerged spontaneously from the community (in an age were internet didn't existed) and later, when it was already a common trope, someone referenced it on some media. Even if that is, and that media reference exist (wich I don't know, but I cannot prove it doesn't), it would just have repeated something that the community was saying for years.