When Castiel burned Michael with holy oil.
Castiel: Hey, a**-butt! (Throws bottle of flaming Holy Oil at Michael, burning him up)
Castiel: He'll be back, and angry, but you got your five minutes.
Lucifer: Castiel, Did you just Molotov my brother... with Holy Fire?
Castiel: Uh... no?
Lucifer: No one d*cks with Michael but me.
(Lucifer snaps his fingers and Castiel explodes)