From an episode of Family Guy where Peter tries to "educate" himself on proper edicate and ends up picking up a New Yorker. Being Peter, he turns to the comic section of the New Yorker and find "I would be more apathetic if I weren't so lethargic." And waits a few days trying to understand the meaning of it.
>"I would like a copy of the New Yorker Please"
>>"Okay"
>"I would be more apathetic if I weren't so lethargic? What?"
>"Ohhh I get it, can I get a jugs?"
>> "Sure thing"
"That's so lemon" is a way of saying something is very cool but slightly off, in the way that eating a lemon or something of that highly acidic or citrusy nature causes one to make /that/ face.
A: That new mansion I bought is so cool!
B: Yeah, that's so lemon! Too bad it's decrepit and beyond repair...
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.