The Milkmonster is a large landbound animal which is characterised by it's ability to consume massive amounts of milk without any gastronomic consequences or concern for others who may wish to keep some of said milk for their own consumption.
Upon finding a supply of milk to have been suddenly and inexplicably exhausted:
"Dear God no! The Milkmonster has struck again!!"
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.