twist是“扭曲、旋转”，Twist someone's arm是把胳膊肘都给拧过来了，形容的就是强人所难的做法，所以twist someone’s arm指的是给某人施压，强迫某人做什么事情。

【例句】
I've really had quite enough to eat,but perhaps if you twist my arm I could have just a little bit more.
我真的吃得非常饱了，不过要是你硬要我再吃也许我还可以吃一点。

You don't have to twist my arm. I told you I would go with you to the shop.
你不必逼迫我，我告诉过你我会一起去商店的。