The act of either :
A) Catching on fire whilst receiving blumpkin
B) Receiving blumpkin whist already on fire
or C) Someone who randomly but quickly (spontaneously) decides to give another blumpkin.
A) "Ohh this blumpkin is so good Karen!"
"WTFFF!! You just spontaneously comblumpkinned!"
B) "Oh shit my johnson's on fire!"
"Here, a little spontaneous comblumpkin will put that right out!"
C) "Dude, my girlfriend surprised the hell out of me yesterday for my birthday."
"Oh really? What'd she do?"
"She spontaneously comblumpkinned me!"