Your gender is not related to your sexual orientation.

no but the way we talk about it is. we typically use vocabulary to describe orientation that is relative to gender identity. that is, a person who is attracted to men is gay if they identify as a man or straight if they identify as a woman.

that said, "transgender lesbian" shouldn't be too hard to parse unless you've been living under a rock for the last fifteen years.

lesbian: woman who is attracted to women transgender: one whose gender identity does not match the sex they were assigned at birth

A transgender lesbian, therefore, is a transgender woman ("male-to-female") who is attracted to women.

I didn't know this was really a thing, I've only heard of it on Mad TV when I was younger

https://www.youtube.com/watch?v=bgcLfohtFbE

This is needlessly malicious. People have made the same argument for non-trans gay people and it's no less gross if you make it for trans gay people.