A chengchi is someone that you believe is acting like an idiot when they really aren't. Many people can be chengchi's, no matter who they are. The term ChengChi (with the exact same uppercases) can also be when you don't want to show someone's name or say they're gender.

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.