Well, this term probably doesn’t exist. Hence, I’ll define it for you.
Nominal idiosyncrasy (n): The phenomenon of an idiosyncrasy getting attached to a particular name of a person so much that it is hard to think of anyone else with the same name. Because of this phenomenon, ordinary proper nouns become adjectives.
I can think of a few. If you can think of more please add them as comments.
Arnab – someone who is a jerk, who would never let anybody else complete a sentence, who never lets anybody else’s opinion seemingly matter; self-obsessed prick.
Anthony – someone who is a politician who will send out semi-obscene messages to young women with attached pictures of himself in his underwear; someone who has just an average penis but thinks that it is bigger than that.
Bill – someone who is a politician whose wife is also a politician; someone who has oral sex with his secretary (such secretaries are called Monica irrespective of their sex); someone who is obsessed with sex.