I memorized my key after my game derped out and I had to e-mail customer support, as I had deleted the key e-mail thinking I wouldn't need it again.
"hey i know my key by heart i'd better delete my backup for no reason at all!"
the only part of my ID i can remember is AAAJD :(
I am so very confused by people like you. Very confused. I have never heard of any people trying to remember a game serial key by heart other than several people in the Blockland community.