1. A throwback to something very pleasurable in one's past.
2. A feeling of absolute bliss because one suddenly remembers something pleasant in one's past
John: I think I just had memgasm
Jilll: OMG, what happened??
John: I just heard "Smoke on the Water" for the first time in like 25 years
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.