They will laugh and think it's funny because they don't get why it bothers people. They'll insist that the only reason what you're doing is wrong would be if you were "reinforcing a lie" or some other bull shit.
The thing is, they don't. Because no one ever put Elliot in the position of literally being told by everyone around her that she was a man, no one ever told her she was delusional and should find a counsellor to investigate whatever trauma might have caused her to have these incorrect beliefs about herself that let her think she's a woman when she's clearly not.
The people complaining don't understand because they think it's at worst as bad as JD saying Elliot has an Adam's apple, and they don't or won't confront the fact that that'snot what they're doing to trans people. And yeah, those jokes were stupid and transphobic and unnecessary, but even then the whole joke is that it's funny she gets upset about it because no one could ever seriously confuse her gender. People can always tell. Right?
They don't understand, and they refuse to consider ideas that would let them, and that's pretty fucking shitty. But honestly? If I could just chalk it up to malice, life would be a lot easier.
That makes sense, but a lot of the same points apply. No one thought J.D. was a girl or told him he was delusional for believing he wasn't. I do get that it was obviously meant to be demeaning there, but almost certainly not for a "you aren't who you think you are" way, but rather "girls are silly and you're silly so you're a girl" way. Casual misogyny: not really better than casual transphobia, but still a separate thing.
The distress JD feels when belittled thusly isn't because someone really believes he is wrong and bad for thinking he's a man, but because Cox doesn't respect him as a doctor and has the erroneous belief that calling him a woman's name conveys that somehow.
Don't do this. Misgendering cis people merely makes it seem acceptable to use misgendering as a weapon in general. I understand the inclination to try and make people understand what it is like... But if they have never doubted your gender, they will not understand.