I'm looking for an adjective which I could use in the following situation for example:
"Don't try to understand the joke Joanne said to George; it's a in-joke between romantic partners."
"Don't try to understand the joke Joanne said to George; it's a [X adjective] in-joke."
Does the X adjective exist? Is it defined in a thesaurus?
P.S. Sorry if the format or nature of the question does not comply this is my first time posting here.