"What did the traffic lights say to the car?" The key words here are traffic lights which change colours from red[ stop] to green [go] "Don't look now. I'm changing!" The key words here are "I'm changing" In your joke, the car and lights have taken on human qualities and the joke is an example of personification.For example the lights could symbolize a woman who says this to a man which is symbolized by the car.

The joke is that "I'm changing!" is a phrase typically said when someone's getting naked and putting on new clothes. It would obviously be very rude to watch someone trying to get changed into new clothes, regardless of how well you know them. So it's a joke on language ambiguity. Lights change colors from red to green to yellow, and the alternative meaning of "change" as a colloquialism for clothes-changing is used to make it seem as though the car's watching the traffic light get naked.

Nanren, you should use the "Answer this Question" button for your comments so that the questioner can mark it as the best answer if they choose to.

It would be impolite to watch while someone changes clothes. Traffic lights are said to change from red to green. . So "change" is taken to mean "change clothes".