Well, this is probably veering well into editorial territory, but I’d say there’s a number of factors in play, here. Not the least in the problem of interpreting an artwork in a different medium (TV and film, I’m assuming you’d mostly be thinking of, here. Unless we want to start critiquing cosplay).
First, context. I mean, in the wrong time and place, a ballgown, a full set of Samurai armor (complete with ornate Mempo and Kaubto), a pressurized flight suit, or a Masai Shuka would look ridiculous. Something that looks intimidating sliding out of the shadows in a dark alley or bathed in brilliant atomic fire might not look that impressive on someone standing around in a public park at noon, or sitting in a conference room.
Plus, to combine the two, what constitutes the work’s stylistic standard of “real life,” even when it’s all live action, is going to effect the result. I mean, Cesere the Somnambulist is going to look as ridiculously out of place in Zero Dark Thirty as a Navy SEAL in full battle-rattle and NOGs is going to look in The Cabinet of Dr Caligari.
Back to the present, at least, the particular type and design of costume is going to matter in how “ridiculous” it generally looks in real life (or the “realistically” stylized cinematic form of real life). Something very utilitarian, for example, or at least appearing utilitarian, is probably going to translate a lot easier to real life, especially the jaded modern eye.
But on that note is also, frankly, fashion. In observing pictures and photographs of the past, and even in my own lifetime, I know for a fact that there are forms of dress were considered proper and desirable in their own time that would be a joke in another era. Or sometimes all other eras. The forces of societal evolution are like a great, intricate fractal pattern that occasionally produces enormous perms and codpieces.
Thus, to some eras, it might seem perfectly acceptable for a live-action character to wear a spandex leotard, or fight bare-chested in a bandana, or lots of bright colors and flourishes. And as much as I’d like to hope otherwise, I can’t really say with confidence that I completely believe it’s playing to the mass audience’s sophisticated tastes and technical worldliness that drives many modern superhero costumes to have lots of segmented armored pieces, accentuated textiles patterns, and rich, darkened colors.
Or maybe I’m just still bitter about bomber jackets not being in style anymore.
Maybe I could boil that all down to, “I find the ‘ridiculousness’ of the character’s costume depends on how plausible I find it to be that the character could be wearing it, considering their actions and the setting and situation; an appraisal influenced by my own aesthetic biases at the time, which are in turn at least heavily influenced by those of contemporary society.”
And if I had a little more sleep or a bit more skill with figures, maybe I could boil that down into a proper formula. One I could plug into a spreadsheet.