Sarcastically Sincere About Being Sincerely Sarcastic

(I am known for being very sarcasm-blind while my dad and brother are sarcastic A LOT. This incident happens while we’re out for dinner. My brother made a sarcastic remark I took at face value and the following ensued.)

Me: “I can never tell when you and Dad are being sarcastic, [Brother]. You’re both so good at being sincere.”

Brother: “I’m sincerely sarcastic.”

Me: “This is going up on NotAlwaysRelated.”