Grand Theft Auto III: San Andreas
Back when I played GTA3: Vice City, I had a strange habit of collecting city buses and storing them in any garage I could fit them in.
When I got GTA3: San Andreas, I found out that the vehicle settings were stored in a flat text file. I found the city bus in the file, and increased its weight, engine power, and durability, lowered its center of gravity, and made a few other minor tweaks. The result was a nigh-indestructable bus.
A video of me playing around with my second version of this bus is shown below: