The abbreviation FAFO usually stands for “Fuck around and find out”, which in most cases can be loosely translated as “Stress around and find out”.
Ye (fka Kayne West): Can I make anti-Semitic comments and worship Hitler? Or will I be banned on twitter if I do?
Elon: Is Tim Cook going to kick twitter out of the appstore?
Student/Employee: And what if I don’t get this done by Tuesday?
Random Guy 1: I wonder if that guy with the brass knuckles is as dangerous as he looks?
Random Guy 2: FAFO!
Jens-Torben Gerstenklecker: I wonder if Mom will ground me today?
Maria-Elisa Gerstenklecker-Prummeklöten: FAFO, Jens-Torben!
It is also often used in software development or technical projects. Then it means as much as “Try wildly, then you’ll see.”
twitter developer: I don’t know how to make this query faster!
The chat abbreviation became popular when Elon Musk tweeted it – probably in reference to Ye (see above).