Totwist someone’s armliterally means to take a person’s arm and turn it around, which could be really painful if you take it exactly word-for-word.If yourarm has been twistedit means that someone has done a great job of convincing you to do something you might not have wanted to to do.
And if you manage totwist someone else’s armit means that you’re great at convincing them, and they’ve finally agreed to do something after you’ve been begging them.
“Jake, you should really come to the party tonight!”
“You know I can’t, I have to hit the books (study).”
“C’mon, you have to come!It’s going to be so much fun and there are going to be lots of girls there.Please come?”
“Pretty girls?Oh all right, you’vetwisted my arm, I’ll come!”