Comedy is the only genre where snark and smart alec comments work. Anywhere else and it will either kill any drama you're trying to build up or kill any empathy you might have for the character.
But let me be clear on what I mean by snark. I'm not necessarily referring to the one-liners James Bond or Arnold/Bruce/Stallone would toss off in their action movies. Done correctly, a one-liner is a statement of masculine disdain or downplaying a challenge that has been met. That's the key. A one-liner is issued before or after an event, not during. Attempting one-liners during a fight is snark and it breaks the audience identification and suspension of disbelief by breaking the fourth wall. I've used one-liners myself, in Smooth Running, but it was in character for Smooth Charles and was not intended to break the fourth wall*.
Snark calls attention to the situation and invites the reader to be as dismissive of it as the character is. That's why it kills drama. If you have your hero tied up and being threatened by your villain, which happens often enough in the Whedon-verse, having them joke and belittle the situation destroys the tension of tying up the hero and putting them at the mercy of a villain in the first place.
That's one of the things I hate about Buffy. It tries to be a drama and a comedy*. A smart alec comment to a real bad guy will cost you some teeth. It might even result in immediate maiming, torture or death. I remember in 20004 when Al-Queda was doing one of their murder propaganda tapes, threatening an Italian prisoner. The prisoner refused to play along with the scripted event, standing up, struggling and saying, "I'll show you how an Italian dies". That was Fabrizio Quattrocchi. He wasn't being snarky, he was being a man. He also died, right then and there, shot in the neck.
So every time one of these tv shows has the heroes tied up and being menaced and the hero mocks them with 'not this again' or some other smarmy pseudo-witty remark, it takes me out of the scene. In real life, the bad guys are bad. In drama, the bad guys should be bad. Bravado should be permitted, even encouraged for some characters, but there should be consequences. Let the villains be villainous. Unless you're making a comedy.