After watching alot of cheap cartoons, theres somethign I am surprised has not been brought up at all when it comes to discussing tomgirl-ism. And that is characters in drag.
A cheap punchline, to be sure, and one that I dont think Chris compleatly understands.
The reason many cartoon writers nowadays occasionally write a bit where a characters in drag is simply for the point of it being a very unfunny punchline, which thenforth makes it funny. Ok look, my point is that humor is very subjective here, and something that Chris does not quite understand. After all, there have been skits in family guy where Peter, for one reason or anouther, crossdresses. And yet quite possibly in Chris's mind the joke of making peter look gay does not cross his mind because to him, sexuality is something taken very seriously, and he cant be gay, I mean, he is happily married with a wife and kids!
So in short, I think part of what fed tomgirlism is the trope of characters being in drag. And it isnt compleatly limited to cartoons, the show M.A.S.H. had a character called Klinger (played by Jamie Farr) who wore a large stockpile of dresses in an attempt to be dubbed insane by the army and go on home. But Chris primarily watches cartoons and he loves family guy, so I am using that as the prime example.