One for the gamers out there, the well known Konami Code, also known (due to its original appearance) as the Contra Code.
Up, up, down, down, left, right, left, right, B, A
I’ve used it, you’ve used it, hell everyone who’s ever had a joypad blister has used it!
Print available in blue, yellow, green and purple. Want another colour? ask and I’ll see what I can do!