Marshmellowing

The act of "Marshmellowing"
Marshmellow - Marshmellowed - Marshmellowing

When a guy Gropes or Licks a girl's Ass or Boobs, or in fiction, Tails and Wings.
Tails and Wings are seen as "Erogenous zones" in fiction, meaning they are incredibly sensitive

the term "Marshmellowing someone" first had the definition of "Accidental Sex" or even "Unknown sex", it Originated in an anime called "To Love-Ru Darkness" where the Main Character was asleep, but was groping the girl's Tail, Boobs and ass, and went on to lick her tail.
The reason why its called "Marshmellowing" is because this whole time, the Main Character was Dreaming about marshmellows, how "soft & yummy" they were, of course, this was actually the girl's soft boobs, and presumably "yummy" tail.
Note: The girl was awake and enjoying herself, basically using him as a sex toy since he doesn't have the Courage to do sexual acts if awake

Sister: Damn that Rito, he's such a stupid Brother...
Father: What did he do now?
Sister: i was going to wake him up, only to find him Marshmellowing my classmate! Why was she even in his bed?