Or vice versa. They will quickly find out that they do have a preferred pronoun
Misgendering cissies doesn’t really work, you never have the full force of an entire societal megastructure wanting to erase their existence to back up your claim, yet they do.
If you want to get them mad, call them cis shits or something like that, people who violently reinforce the status quo hate being reminded that they could exist as anything but the default.
most people aren’t terminally online so i think that would just force me to explain what cis means.