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

:  a brief oral narrative with a climactic humorous twist

:  the humorous or ridiculous element in something

:  to make jokes :  jest

:  to make the object of a joke :  kid