By the Lord, I knew you as well as he that made you. Why, hear you, my masters, was it for me to kill the heir apparent? Should I turn upon the true prince? Why, thou knowest I am as valiant as Hercules, but beware instinct. The lion will not touch the true prince. Instinct is a great matter, I was now a coward on instinct. I shall think the better of myself, and thee, during my life—I for a valiant lion, and thou for a true prince. 
(Act 2, scene, 4, lines 278–86)

During the Gad’s Hill robbery, Harry and his friend Poins played a trick on Falstaff and stole the money from him that he had stolen from a group of travelers. They played this trick knowing that Falstaff would tell them a hugely exaggerated version of the story the next day. Now, true to character, Falstaff claims that he fought off a great number of attackers. But when Harry reveals that he was in fact the one who defrauded him, Falstaff immediately utters these words. Changing his story, he now claims that he knew it was Harry all along, and this is why he didn’t fight back properly. Falstaff shows his nimbleness of mind in being so quick to alter his story. He also demonstrates his cleverness when he likens himself to the proverbial “lion” that cannot harm the “true prince.” Falstaff is full of such amusing excuses, which entertains his friends.

Falstaff: Do thou amend thy face, and I’ll amend my life. Thou art our admiral, thou bearest the lantern in the poop, but ’tis in the nose of thee. Thou are the Knight of the Burning Lamp. 
Bardolph: Why, Sir John, my face does you no harm. 
Falstaff: No, I’ll be sworn, I make as good use of it as many a man doth of a death’s-head or a memento mori
(Act 3, scene 3, lines 25–32)

Falstaff’s comrades find special delight in making jokes about his large size. Here, Falstaff shows that he is equally equipped to trade insults. He exchanges lines with Bardolphe, who has a reputation for drink. In fact, he drinks so much that his nose is red and enflamed. Thus, when Bardolph makes fun of Falstaff for his weight, Falstaff returns immediately with this joke about Bardolph’s discolored face. He implies that his companion’s nose is so red that it burns as bright as a lantern that allows a ship to make its way in the dark. Falstaff then goes on to liken Bardolph’s face to a “death’s-head”—that is, a skull used as curio meant to remind people of their mortality (i.e., “a memento mori,” or reminder of death). Though said in jest, Bardolph is evidently chastened by Falstaff’s quick-witted retorts.

‘Sblood, ’twas time to counterfeit, or that hot termagant Scot had paid me scot and lot too. Counterfeit? I lie. I am no counterfeit. To die is to be a counterfeit, for he is but the counterfeit of a man who hath not the life of a man; but to counterfeit dying when a man thereby liveth is to be no counterfeit, but the true and perfect image of life indeed. The better part of valor is discretion, in the which better part I have saved my life. 
(Act 5, scene 4, lines 115–23)

Falstaff utters these words in the midst of the Battle of Shrewsbury. During the scene in which Hotspur and Prince Harry fight in single combat, Falstaff engages in a brief scuffle with the Earl of Douglas. Falstaff falls to the ground and plays dead. Then, after Harry has slain Hotspur and left the field, Falstaff rises from the dead and delivers these lines. In his characteristically witty way, he plays on the idea of a counterfeit. He reasons that his playing dead doesn’t make him a counterfeit. On the contrary, the real counterfeit is the man who actually dies but looks like he could be living. This paradoxical logic is amusing, and once again it demonstrates Falstaff’s wit. Yet it also offers another example of his dishonorable conduct. He will follow any line of reasoning that justifies his actions—even when he’s alone on a battlefield.