I’m not sure that you do. Pretending to not understand something you then say that you did understand is not sarcasm. It’s more like feigned ignorance. And while I guess that can be used to point out that something is unclear, in this case the thing was clear, so the ‘joke’ didn’t really land
yyyyyyep. And I can never figure out if I’m depressed or just sad about the state of things for valid reasons.