Johnny learns a moral

The teacher tells the students to go home and learn a moral for homework. The next day the teacher started with Sarah asking her what moral she learned.
"I was helping my momma bring in the groceries and the bag ripped and I dropped the milk and started to cry and my momma said "don't cry over spilled milk".
The teacher told her that was good and gave her a B. Next she called on Michael.
He said " All day long I was thinking about all of the candy I had in my drawer and how I was gonna eat it all but when I got home I found out my brother ate half of my candy. I told my dad and said " never count all of your chickens before they hatch".
The teacher being impressed with his story she gave him a B+. Now she picked Johnny.
He starts off with" One day my father was in the war stuck in a foxhole with a gun with 10 bullets, 2 hand grenades, and a fifth of whiskey". The teacher gives him a glare and he he continues on with his story. " Well first he drank the whole fifth of whiskey in five huge gulps and stood up and threw one grenade killing five people and threw the second one killing seven more people then he stood up and killed a person with every bullet with the gun".
The teacher looked at Johnny and asked him" What moral did you learn from that"?
Without missing a beat Johnny said "The moral of the story is...Don't fuck with my dad when he's been drinking".