play a joke on vs fob

play a joke on is not a noun while fob is a noun.

Word	Noun	Adjective	Verb	Adverb
play a joke on	No	No	Yes	No
fob	Yes	No	Yes	No

As verbs, play a joke on and fob are synonyms defined as:

Other synonyms of play a joke on include flim-flam, fox, play a trick on, play tricks, pull a fast one on, trick.

play a joke on (noun)	fob (noun)
	short chain or ribbon attaching a pocket watch to a man's vest
	an adornment that hangs from a watch chain
	a vest pocket to hold a pocket watch

play a joke on (verb)	fob (verb)
subject to a playful hoax or joke	deceive somebody
deceive somebody