Just watch the video.
And here's the thing in 1.3.2 multiplayer:
Unleashing rage only possible with bare chest and empty hands. Drains a lot of stamina / hunger. For real men only.
You know that you can use Kenshirawesome if you see your second fist waiting on the lower screen edge.
Hit entities movement and attack strenght will be crippled with each strike, Creepers can no longer explode, and Skeletons can no longer shoot you.
To let your fists fly make sure you meet the requirements (chest-fists-hunger) and hold MOUSE2. The kick of justice is done by jumping and tapping MOUSE2. The kick also drains stamina, but less.
Your iron fists can smash through most materials beneath a certain hardness.
See official Site for changelog, more info, instructions.