Billy Costigan: [to Frank Costello] You accuse me once, I put up with it. You accuse me twice... I quit. You pressure me to fear for my life and I will put a fucking bullet in your head as if you were anybody else. Okay?
[Frank drops something. He reaches under the table and pulls up a gun. He looks at it as if he's never seen it before and then points it at Billy]
Frank Costello: You got something you wanna... ask me?