Kiss and tell
Publicly retell of one's sexual exploits, often with the aim of revenge or monetary gain.
Kiss and tell is of course a euphemism - firstly, when stories of this sort arise we can take it for granted they will include details of more than just kissing. Also, if as is often the case now, they are printed in tabloid newspapers, sell would be a more appropriate word than tell. It might be thought to be a recent phenomenon, but it dates back to at least the late 17th century and appears in Congreve's play Love for Love, 1695:
Miss Prue: Look you here, madam, then, what Mr. Tattle has given me. How sweet it is. Mr Tattle is all over sweet, his peruke is sweet, and his gloves are sweet, and his handkerchief is sweet, pure sweet, sweeter than roses. Smell him, mother - madam, I mean. He gave me this ring for a kiss.
Tattle: O fie, Miss, you must not kiss and tell.
Miss Prue: Yes; I may tell my mother.
It isn't entirely clear whether the meaning of kiss and tell there is the same as our current usage. The play does imply that noisy kissing is like kiss and tell, presumably because everyone hears it. That does seem to suggest the meaning as we now understand it. The lack of any explanation of the term in the play also suggests that it would have been expected to have been known to the audience - so we should assume a coinage prior to 1695. The phrase didn't become widely used at the time though and I can't find another reference to it for over a century. That's in The Marysville Tribune in June 1856:
"She kissed me then she fled"... "But I never kiss and tell."
Kiss and tell continued to be used occasionally until the mid-20th century but has become more public since then. In 1945, Hugh Herbert's comedy of adolescence Kiss and Tell was made into a film and this gave the phrase something of a boost.
It is only in recent years though that payment for salacious stories about prominent people has come to be called kiss and tell. In 1963, Richard H. Rovere wrote a review of Emmet John Hughes' The Ordeal of Power: A Political Memoir of the Eisenhower Years for The New Yorker magazine:
The Ordeal of Power... is a political memoir... of highly questionable taste and propriety. It is a kiss-and-tell book.
The exposures made in that book were political rather than sexual in nature, but the implication of confidences betrayed in the pursuit of book sales is clear.
Kiss and tell is now a style of journalism, otherwise known as 'cheque-book journalism'. Many high-profile celebrities now oblige prospective staff, and even prospective spouses, to sign non-disclosure agreements which bar them from making any private knowledge they have of the prominent person or their lifestyle public. This also dates to the 1960s, for example, this piece from The New Statesman, May 1963:
"Newspapers should come to a self-denying ordinance to abandon the cheque-book journalism of confession stories by criminals, prominent divorcees and others who have won notoriety."
Of course, that didn't happen and now in the 21st century we see tabloid newspapers printing invitations for anyone who has any gossip about some celebrity or other to contact them. In the UK ate least there is also a new career path for young women, which many are following - offering sex to men in the news in order to sell their story later.