What was Big Willy Shakes going for?
It may not look like it, but Pistol's line is actually a threat. He's saying if Falstaff doesn't give him the money he wants, he'll use his sword to persuade Falstaff (or anyone else for that matter) to give him the cash. Falstaff gets up in Pistol's face and says he's tired of always having to bail out Pistol when the guy gets caught stealing. Then he orders Pistol to scram and yells at him for refusing to deliver his letter to the "merry wives."
And Pistol backs down. In case you hadn't noticed, Pistol is a hothead (duh, he's named after a firearm), but he's all talk. He says he's ready to rumble and use force in order to get his piece of the pie, and yet, the funny thing is, we never actually see him throw down with anyone in this play.
But the damage is already done.
Falstaff gives Mistress Quickly a little monetary tip just before she runs off. Pistol is not happy that Falstaff just gave Mistress Quickly some money and can't spare any for him. He calls her a "punk," which is fun Elizabethan slang for "whore," and storms off.
So Pistol is furious and he's threatened Falstaff with his sword. Turns out "the world is mine oyster" this isn't just a sweet little catch phrase we found stitched on our grandmother's pillows. This is the first time this phrase appears in print though, so, Shakespeare either invented it or, at the very least, made it popular.