Dongsaeng is a Korean word describing a family or friendship relationship. It is used to refer to one's younger sibling or a close friend that is younger than oneself.
"I promised my dongsaeng I'll treat her for dinner if she did well on her test."
(Although the above statement is a command, 'dongsaeng' acts as a form of endearment like 'little brother' or 'little sister'. In other words: "Lil' bro, how about a cup of coffee for your big bro?")
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.
A lighthearted reaction upon receiving disappointing news of some sort. Usually something that isn't a particularly a big deal, esp. when it primarily affects someone else - sort of a mild schadenfreude. Sometimes doubled or tripled, and possibly said in a sing-songy voice for added comedic effect to imitate a muted trumpet, which is how the meme originated.