你好! First I should say I don’t like this sentence. I hope you never use it. But I can tell you the difference between “xiang” and “yao”. Literarily speaking, “xiang” means " would like to", and “yao” is " to want". So you can see, “yao” sounds much stronger than “xiang”. If you heard one people said " Ni xiang si ma?" , it doesn’t mean he or she really want somebody go to die, just a warning in a bad way.

谢谢你的支持（support）! Any questions just Ask Benny and me.