People are fighting in a war, and a man gets hit four times in the arm and says, "'Tis but a scratch!"
And the other guy, looking at him in shock, says, "A scratch? Your arm is off your body!"
Okay, so listen up, nimrod. The dude in the joke is losing his arm but acts like it's nothing! It's funny because it's so unrealistic. It's like when you stub your toe and act like you need an ambulance... only way, way more extreme. You probably think getting a paper cut is worse than losing an arm, huh?