Boulder Dash
A family friend bought this for our family on the C64 and then my dad got super addicted to it, he was up until 2am most nights trying to crack the game. He would leave work early (he ran his own business) to come home and play it. It also meant no-one else could play the computer or watch TV.Eventually, I took a biro to the tape, sorry dad, and scribbled across it, which seemed to break it. Finally we were free.