private joke

: intended for or restricted to the use of a particular person, group, or class

: belonging to or concerning an individual person, company, or interest

: restricted to the individual or arising independently of others

: one not in public office

: privacy

: private parts

: something said or done to provoke laughter

: the humorous or ridiculous element in something

: an instance of jesting : kidding

: to make jokes : jest

: to make the object of a joke : kid