It's when something is so mind-numbing, your face uncontrollably spasms into some sort of an ahegao, not out of arousal, but your brain malfunctioning. As if your brain is getting licked.
A similar thing can occur with extreme ASMR tingles, like Japanese ear-licking ASMRs.
*insert feather into your ears*
"Gwah-uah!! God dammit! Quit it!"
"Ahahaha! Your face pulled a retardao."
A combination of the words "retard" and "nation".
A nation or defined group of people that seem mentally retarded, stupid, or "special"; A cluster-fuck of stupid people.