Russian Roulette Introduction

Alright, listen up, you smooth-brained chucklehead. You see, the joke plays on the different kinds of "roulette". Your friend enjoys the casino game, which is all about chance, but then you go and introduce him to Russian roulette which involves a gun. The punchline is that the friend's mind is blown, which is a phrase that can mean very impressed, but also dead in this case. The humor is dark because you're implying you killed your friend.