It's like a shower thought, but when the thought has started outside of the shower, then dwelled on through various iterations (like when you keep hitting next until you get to the weird part of YouTube), and then proposed to your friends as a serious question.

n. The birth name of somebody who has changed their name. Most commonly attributed to trans people, but can be attributed to any person who has changed their name. (sometimes written as two words: dead name)

v. 1. To call somebody by their deadname.
v. 2. To out somebody's deadname to the public.