It means that the other person is being incredibly stubborn or foolish, choosing some stance or action that's absurd. Could also be an expression of frustration about someone.
翻译成中文就是“不可理喻”的意思。
来两个例句体会一下：
Alisa told me that she has to leave the job because her boss is really impossible.艾丽莎告诉我，她必须离职了，因为她的老板非常不可理喻。 The actress is impossible on the set, so no one likes her.这个女演员在片场太不可理喻了，没有人喜欢她。
在美剧《生活大爆炸》中，Howard经常惹Raj生气，有一天他们两个又吵了起来： Raj: And you do it all the time. Last week in the mall at Radio Shack, we were looking for a phone with giant numbers for your mother, and I suddenly realize you're not even there.Howard: Getting shot down by the girl at Hot Dog on a Stick. But in my defense, she was gorgeous!Raj: You're impossible.-你一直都这样，上周在Radio Shack商场，我们在帮你妈找一部超大号码键的电话。而我一转眼，你居然就不见了。-我被HDOS快餐店的一个女孩儿勾走了，听我解释，她实在很火辣嘛。-你真是不可理喻！
要表达“不可理喻”，还可以用这两个地道表达：you are unbelievable 和
you are unreasonable，例如： -Let's break up.-Why? You are really unbelievable!-我们分手吧。-为什么？你真是不可理喻！ What a stupid idiot! You're unreasonable.你真是个白痴，不可理喻！
