It is, when you think about it, a little interesting that Larry Linville wasn’t wrong when he left M*A*S*H because there was nowhere else for them to develop Frank Burns at the same time that The Rockford Files was making Angel Martin the most psychologically complex character on the show. The pair have any number of traits in common, you see; they are both examples of the Pop Culture Weasel. The important thing to understand about the character, though, is that there are ways to give the Weasel dimensions that not every version of it does.
Oh, there are some definite basics. Your standard Pop Culture Weasel has to be primarily out for himself. (There are female variants, but we’ll mostly be talking about the men here, and goodness knows they’re more common.) He may have an object of affection, but that doesn’t mean he takes that person seriously as a human being with their own wants and needs. Indeed, he can’t take anyone seriously as a human being with their own wants and needs. This is either because it genuinely doesn’t occur to them, because they believe that giving someone else what they want prevents the Weasel from getting what he wants, or because they assume that everyone wants what they want and choosing something else would be unthinkable. The Weasel must be a bit of a sociopath and a bit of a coward.
When Angel chooses how to treat someone, it’s because he assumes he’s only doing what that person would do in his shoes, no matter what that thing is. When Chester Tate of Soap treats someone a certain way, it doesn’t even feel like a choice—Chester simply doesn’t think about not doing the thing he wants to do. When Ted Baxter of The Mary Tyler Moore Show does it, it’s because he’s not bright enough to realize there’s another choice. That’s another similarity in the Weasel; he’s never as smart as he thinks he is, and it’s easier to get the better of him than he’s capable of remembering.
I think the ’70s were the Golden Age of the Pop Culture Weasel. He was mostly a feature of comedies, because if you can’t laugh at the Weasel, you’re reduced to thinking how awful it is to have one in your own life. In the ’70s, it was seen as okay to laugh at some substantially darker things, and people weren’t always expected to have a Redeeming Feature. By the ’80s, you were getting the occasional Dan Fielding, but even Dan was actually as smart as he thought he was and was sometimes shown to not be irredeemable, though he was awfully close.
And, no, womanizing and misogyny are not necessary features to the Weasel. Angel almost gets married once and still seems more scared of women than attracted to them—Angel is, at his heart, scared of everyone, after all. Ted Baxter ends up actually getting married, and to a pretty decent woman who honestly deserves better. Heck, even Frank Burns seems more a serial bigamist than anything else, having an affair with his receptionist Back Home and with Margaret while in Korea. Sure, okay, he’s kind of a misogynist, but as with Angel and his cowardice, it’s more misanthropy. Frank hates people, and no one more than himself.
If Frank had been competent, he could’ve been redeemable and honestly still a doable Weasel. There are certainly competent Weasels—in The Million-Dollar Duck, Tony Roberts plays Fred Hines, a friend of the Dean Jones character, who’s a Weasel and good at what he does. You can even have Weasel heroes; Disney had one of those in Mr. Donovan of The Apple Dumpling Gang, among others. You do tend to redeem a Weasel hero, but that’s still a Weasel with the roots of redemption in him. Frank didn’t have that, and his psychology wasn’t as developed as Angel’s. Who can blame him for not wanting to keep at it?
Weasels are almost always cheap, too; be better and contribute to my Patreon or Ko-fi!

