Why, then the world's mine oyster.
Many people quote this, but in the play it's better. Falstaff fires Pistol, his servant, and refuses to lend him money. Pistol decides to fend for himself. Fastaff is being witty, at his own expense: Pistol will betray him.
Enter FALSTAFF and PISTOLFALSTAFF
I will not lend thee a penny.PISTOL
Why, then the world's mine oyster.FALSTAFF
Which I with sword will open.
Not a penny. I have been content, sir, you should
lay my countenance to pawn...