No matter how hard I jerk the Right Analog to the left, I still lose. Can anyone help?
You're supposed to go left and right, over and over again. I used to lose all the time too, but then realized that you don't have to move the stick to the extreme right and left, just a little in each direction. Try that and it should be easier. Also, you don't have to arm wrestle your friends for 100%; you can arm wrestle anybody and still get it. Just wrestle some random guy. Arm wrestling friends and arm wrestling deadbeats is harder.
My advice is to arm wrestle sparingly. It can't be good for the controller. I arm wrestled to get 100%, and am now not going to touch it again. There really should have been better arm wrestling controls. It's not worth breaking a stick over.