It's about when stuff like nukular bombs or yellow cake get spread around by evil doers.
"Yeah, I've thought about nukular perif-perifu... waitasec... nukular perifulation... whatever. It's hard. But I know it's a bad thing. It's a really bad thing, and it's just not good for the American people. And I'm gonna make damned sure Iraq stops doin' it, before it comes over here in the form of a big hairy mushroom cloud." --George W. Bush
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.