when you go around looking for reindeer decorations during Christmas season and when you find them you balance one's front on the other's back, in a sex position.
"Yo, let's go mounting tonight! I saw some reindeer in Mrs. Robinson's lawn"
"It feels wrong when you mount a baby reindeer on an adult reindeer"
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.