I won't lie, I didn't come up with this.
Why are fire trucks red?
Fire trucks have 8 wheels and 4 people,
and 4+8=12,
12 inches is a foot,
and one foot is a ruler,
and Queen Elizabeth was a ruler,
and Queen Elizabeth was also a ship,
and the ship sailed the seas,
and fish live in the seas,
and the fish have fins,
and the Russians fought the Finns,
and Russians are red,
and Fire trucks are always Russian around.
Therefore firetrucks are red.