Used mostly in anime and manga, the term
growing mushrooms refers to when a character has become immensely depressed or
saddened. The character is often shown to literally grow mushrooms on their body,
signifying that their soul is, for the time being, in a dark and dank place. (Mostly occurs with more dramatic and over the top characters who can't stop crying every 2 seconds 😒)
Senpai: (crying because the girl of his dreams thinks he's dramatic and
egocentric)
Girl: "Senpai, quit
growing mushrooms around me; the smell is absolutely noxious!"