An acronym of M I F O S which stands for Maybe I Am Full Of Shit. It is usually attached to the end of an online post as away of indicating that whilst you currently believe what you are saying you are entirely open, in light of new or better evidence to accept that your argument / comment is invalid
MIFOS is used to prevent potential flame wars and online arguments as it removes the emphatic certainty of the poster and acts as a way of saying that you may be wrong
I still think Jesus was just a very very extraordinary man and not the son of God but MIFOS
I still think Jesus was the son of God and not just an extraordinary man but MIFOS
I personally think ghosts don't exist and would like to see good evidence to make me think otherwise but hey MIFOS
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.