An expression of disappointment. Usually used by little old ladies who were taught not to use foul language. The phrase is even more effective if you have an English or British-type of accent.
Little old lady in a DVD store: Do you happen to have any Rowan Atkinson (Mr. Bean) movies that I could purchase?
Store Clerk: No, sorry ma'am, we are all sold out right now!
Little old lady: Well...dirty rotten old cream of wheat!
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.