Fender bender

 A "Fender Bender" is a term for an auto accident, generally a not very serious one. 

Obviously, this expression references protective covers for a car’s wheels. Older cars once had prominent fenders covering the wheels that were vulnerable to side impacts. Having owned a classic Volkswagen Beetle back in my youth, I can attest to the vulnerability of the fenders to scrapes and hits.

The term "fender bender" originated in the late 1950s. Its appeal is at least partially due to the rhyming nature of “bender” and “fender.” 

Of course, there are lots of other fenders. Fenders on bikes and motorcycles, on western saddles, inflatable ones on the sides of boats to protect them in docking and in front of trams. In British English, the fender is called the wing. 

Interestingly, the word “fender” dates back to the 13th century, initially as a shortened form of “defender”. Originally it was the fender hung over the side to protect the hull of a ship. It was also used to refer to part of fireplaces since the 1680s. It has been used with automobiles since 1919.