An activity or object that is fun, yet dangerous. From the television show Stella, which ran for one season on Comedy Central. It originated in the episode "Camping," in which Michael Ian Black, David Wain, and Michael Showalter have a conversation with a mysterious mountain man.
Mountain Man: Yes, the woods are fun.
Wain: Like boobs?
Mountain Man: But they can also be dangerous.
Showalter: Like fire boobs?
Jim: I dunno, dude, it could end up being like fire boobs.