1. Expression：Dear John letter
Explanation：A letter sent, typically from a woman to a man, to end a romantic relationship.（绝交信）
Example：Mike was clearly upset when he received a Dear John letter from his girlfriend, Caroline. He thought their relationship was going well and didn't expect it to end so suddenly.
Mail call was usually a happy time in the military barracks, except for the unlucky soldiers who got Dear John letters from their sweethearts back home.
Her Dear John letter finally caught up with me while I was awaiting discharge.
By the time he got the Dear John letter from his girl friend, he was climbing the walls.
2. Expression：hit the John
Explanation：To go to a toilet to urinate or defecate. （上厕所）
Example：Be right back, I've gotta hit the John.
Excuse me for a minute——I must hit the John before we go out.
3. Expression： stage-door Johnny
Explanation：A man who spends a lot of time at a theater so as to seek the romantic attention, favor, or company of an actress.（经常去剧院捧女演员的男子）
Example：Ms. Gabler is such a stunning beauty that she always has some stage-door Johnny or another waiting for her after the curtain falls each night.