In that message, you need to look not only at "wrist" but " / wrist". " / " means slash, so what they are saying is that they will "slash wrist", which is another way of saying they will commit suicide. It would probably have been better for you to reply that you didn't understand what "/wrist" means than to say ok. After you replied that it was ok for him to commit suicide, they responded with an insult, "chinks" which is a derogatory term for Chinese people.

其实我也不懂那句话！ 没看到过人那样说。 要是楼上没错，那你朋友说的哪句话说的不对。 就算是自杀的意思，那可以把那句话理解成“我为了可以自杀就和我女朋友分手了”， 真没意思，后来他也骂你，不要理他。