Frank's entire plan for payback against Howard Saint, the man who ordered the execution of his family. First, he gets Saint's business partners angry by costing them a load of money via sabotaging drug deliveries and tossing laundered money into the streets from a high-rise. Frank later sets up Saint's bodyguard and best friend, Quentin, so it appears as if Quentin's having an affair with Saint's wife — all with the help of one of Saint's low-level mooks. Quentin is eventually killed by Saint, who also murders his wife — even though she tells her husband that Quentin's gay and there is no affair. After Saint kills his wife, he calls his son and a group of his closest associates to his nightclub — where Frank picks each one of them off one-by-one, leaving Saint's son for last. (His "punishment" is particularly amusing in its own right.) After taking care of Saint's entire operation, Frank nails him in the gut with a single shot as Saint tries to flee on foot — then he shows Saint all of the evidence of his setup.
Frank:*tosses pictures of Quentin kissing another man* I made you kill your best friend. *tosses one of Saint's wife's earrings* I made you kill your wife. And now, I've killed you.
After the big reveal, Frank sends Saint to a fiery death by chaining him to a car which he then blows up, along with a large number of other cars in the same parking lot. From the air, the resultant blaze looks like a giant flaming skull.
Just before that - during the reveal itself, right after Frank tosses Saint one of his wife's earrings, Saint can do nothing but utter a sad groan. After which Frank then says he's killed him - it's that moan that really sells the moment. He might not have been physically dead - but Frank sure as hell broke him to the point where he might as well be.
When Frank ends up Robbing Saint's main bank in order to stir up trouble between him and the Toro brothers. The launderers he has at gunpoint tries to smugly threaten him to no avail, before he makes them pour the remaining money onto the street.
Launderer #1: Do you know who's money this is, do you know who's building it is?
The Punisher: Howard Saint.
Launderer #2: He's gonna fuck your life up!
The Punisher: He's already fucked my life up.
The fight with the Russian. Bordering on CMOF given how over the top it is, but it's one of the few times Frank finds himself in serious trouble and barely survives it.
Dave gets one when he doesn't give up Frank's location to Saint's goons, despite getting his many facial piercings forcibly ripped out with a pair of pliers. And he doesn't take it like a boss, either; the poor kid is wailing and crying in agony the whole time, and yet neither he nor Bumpo (who was Forced to Watch) tell Quentin anything. After Frank rescues them and asks Dave why he went through that hell to protect Frank, this is the answer he gets:
Harry Heck tells The Punisher that he's a "dumb son of a bitch" for bringing a knife to a gunfight. Turns out that it was a ballistic knife....
Frank's manifesto towards the end of the movie, as he accepts his fate:
I leave this as a declaration of intent, so no one will be confused. One: "Si vis pacem, para bellum." Latin. Boot Camp Sergeant made us recite it like a prayer. "Si vis pacem, para bellum - If you want peace, prepare for war." Two: Frank Castle is dead. He died with his family. Three: in certain extreme situations, the law is inadequate. In order to shame its inadequacy, it is necessary to act outside the law. To pursue... natural justice.
This is not vengeance. Revenge is not a valid motive, it's an emotional response.