Oh, it’s more than rude - it’s blatantly transphobic, and your“flippant” character is a bigot. It’s not about“sensitive language,” it’s about respecting people as human beingsand not forcibly outing a trans person to strangers that might harm or kill them.
This is not an okay thing to happen unchallenged, and it’s definitely not an okay way to out a trans character to the reader.
If this doesn’t need to happen, take it out. I am very rarely definitive about such things, but the way you’ve worde...