Rock

"Ok stepbro, rock, paper, scissors..."

"...Shoot"

You play rock. He plays scissors. The scissors aren't the only thing about to get crushed.

He looks up at your face with fear. He seems to be about to open his lips to say something, while you have drawn your left leg significantly back. Just as he begins to utter a syllable, you snap your foot, your toes flowing forward to just behind his testes, your gracefully arched foot jamming his sensitive bits right up into his throat. In the silent air, you hear them squish. He probably should have worn a little more than boxers.

He is completely unable to finish his thought as the nut pain immediately overwhelms him. For a second after impact, your foot remained at the target. He peered down in shock at this, just as you pulled out, taking a few steps back to regain your footing.

He's bending over and coughing, it doesn't look good at all. Any second now he's going to vomit, and he probably shouldn't even be trying to stand. He collapses down and curls up on the ground, heaving. It's hilarious.

"What's the matter stepbro, I thought you weren't allergic to nuts?" You giggle. He might as well not hear you.

You notice him pee his pants while he's vomiting on the ground. Maybe he should have anticipated you playing rock.