Everyone agrees that fanfic characterization is sometimes wrong. No one can agree on when it’s right.
With comics, Natasha’s sense of humor is going to depend quite a bit on who’s writing her— she had some cutting “contemporary” quips under Stan Lee and the droll wit Warren Ellis tends to give his protagonists. There was a period in the very late nineties and early 2000s when they did try to recast her as humorless. Not as an emotionless robot, but as someone too full-up with passion and tragedy and comic book dialogue to have much room for humor. I’m glad they’ve mostly abandoned that tack, though sometimes the return to winking James Bondian puns has been… questionable.

“Besides, I never get between a man and his… meat.”
I actually think Paul Cornell got this one thing right in a lot of his interviews. “She’s been very different people all through her life, but always deadly, and, I like to think, funny. Not in a one-liner way, but with a very dry, somewhat cynical, wit.” There’s a fatalism to her character that kind of necessitates a certain morbid humor. It’s not a defense mechanism— it’s survival. She’s seen a lot of bone-white awful things, things that have really touched her. To weather the storm she’s had and not come out at absolute zero, she must have learned to find some of it fucking funny.
In the MCU I’m not sure how that’s even a question— everyone’s some degree of quippy in a film scripted by Joss Whedon. “I don’t see how that’s a party,” is a joke, people, she’s not honestly confused about whether or not the flying alien centipedes have come to boogie down. She also smiles at points. Really, I swear.
Panels from Black Widow #5.
