A person who ruins a story someone else is telling, by breaking in with an impatient question, or by blurting out a guess at how it ends.
Janice: "So I'm at the grocery store and this guy I never met before takes my hand and--"
Chuck: "And he proposes, right?"
Janice, "Man, are you a story killer or what?"
Chuck: "And he proposes, right?"
Janice, "Man, are you a story killer or what?"
by Zwieback February 8, 2016