A condition whereby an individual has encountered entirely too much gnarly action (usually skiing/boarding) in one day or thrown down an incredible trick in the park.
"Man the conditions were so epic I caught gnarmonia out there!"
"You see that 10 that guy just threw fakie? He's gonna come down with gnarmonia for sure"
This is what occurs when the right proportions of being sweet, semen, a squirrel, and iced tea have a kid. So far there is only one known to man and he if prolly having sexual intrecorse with your mom at this very moment