Well, it really bothers me when people are so demanding for evidence a character is trans, as if they want the character to, as someone has already put it, turn to the camera and say "oh, I'm trans."
It also really pisses me off when people try to use "but they could be non-binary or agender or gnc" but only when someone insists a character is trans (and spoiler alert: I consider the first two trans anyways, they aren't cis after all so they're trans. You can escape the gender binary of male and female but cis and trans is a different categorical binary altogether).
But for fuck's sake, if you wanna say "I think they're non-binary!" Or any of the other arguments used, you can do it without trying to shut down people who think they could be trans