Echo Two-Seven Tooter

Almost feared as much as the enemy bullet was the "Dear John" letter. Hardly a week went by without somebody getting one. Marines in Vietnam often referred to mail call as the "Dear John" roundup. They were almost always the same story. A guy would get a letter from his girl informing him that she didn't want to hurt him but she'd met someone else and, from now on, she just wanted to be friends. Since they hadn't seen each other in seven or eight months, how could he expect her to be faithful for an entire year? After coming to terms, Marines would began to counsel other Marines who got them by telling them to look at it as a blessing in disguise. Any woman who didn't have enough strength of character to stand by her man in his time of need wasn't worth going back to anyway.

Dear John letter

A letter from a romantic partner, informing that the relationship is over. Usually precipitated by the instigator's meeting a third party.

One Marine is still carrying the Dear John letter he got from his high school sweetheart in Vietnam forty years later.

Etymology
While the exact origins of the phrase are unknown, it is commonly believed to have been invented by Americans during World War II. Large numbers of American troops were stationed overseas for many months or years, and as time passed many of their wives or girlfriends decided to begin a relationship with a new man rather than wait for their old one to return. As letters to servicemen from wives or girlfriends back home would typically contain affectionate language, a serviceman receiving a note beginning with a curt "Dear John" (as opposed to the expected "Dear Johnny", "My dearest John" or simply "Darling" for example) would instantly be aware of the letter's purpose.

There are a number of theories on why the name John is used rather than any other. For starters, John was a common name in America at the time. John is also the name used in many other terms that refer to an anonymous man or men, such as "John Doe" or "John Q. Public". Further, there existed prior to World War II a radio program starring Irene Rich which was presented as a letter written by a gossipy female character to her never-identified romantic interest. It was both titled and opened with the words "Dear John", and may have contributed to the genesis of the term.

In more recent times, women have come to be subjected to such impersonal break-up letters as well. These are referred to as "Dear Jane" letters. Today, a "Dear John" letter is also sent by email and text message.

A Marine stationed in Afghanistan recently received a "Dear John" letter from his girlfriend back home. It reads as follows

a must see, the absolute best ever response to a Dear John letter
Leave it to the Marines!