When a driver of the opposite sex as the passenger calibrates the heat settings in an automobile to full heat output, and positions all blowers to point in the general direction of the passenger.
Hot car is successfully reached when the occupant claims, "My skin is burning". Attempts by the passenger to re-calibrate heat settings to a more comfortable level is met with a sturdy slap on the hand.
The use of the word "blue" to refer to sexually explicit content was first recorded in Scotland in 1824. "Blue" meant "lewd" because prostitutes dressed in blue gowns.