tengdamömmubox

Etymology
From 🇰🇲, the joke being that one could store one's own mother-in-law in the car's rooftop cargo carrier during family trips, thus being able to fit the entire family in the car with the added benefit of not having to deal with a nagging mother-in-law. First seen in print in 2001.

Noun

 * 1) a car rooftop cargo carrier, a car top carrier

Usage notes
While this word was originally a joke, it placed itself firmly in the language and is today usually used as a general word, one that neither has any jokeful connotations nor indicates negativity towards mothers-in-laws. In formal contexts, "farangursbox" is preferred.