the term derived from the series My Little Pony: Friendship is Magic Season 3 Episode 1, where after battling King Sombra Shining Armor's horn becomes covered in black crystals. Thus making him incapable of performing magic.
likewise the "King Sombra Curse" would be similar to Shining Armor's dilemma, but instead with a penis.
"So how'd it go with her last night man?"
"bad, turns out I have the King Sombra Curse"