Advice for friend with autism

*trigger warning - this post mentions self harm/suicide*

I hope it's ok to post this here! A few months ago I made a new friend and they have autism. They are several years younger than me however we have a lot of banter together and speak daily. My issue is that I feel that they're crossing the line too much now. I've observed them swearing at home and insulting family, and also to some of their other friends. Our friendship came about from a mutual enjoyment of insulting each other but in a joking way. Now, however, they often tell me to kill myself or to slit my wrists. They've also told me before that they hope I die in a car accident, which touched a nerve as I was involved in a car accident a few years ago (non serious) but it's still something that troubles me. I asked them if they spoke like this to other people but they said that they didn't, they only said this to me. I don't have the greatest understanding of autism so was wondering if anyone could offer insight into this or advice for what I should do about it? I enjoyed being friends with this person but being told to kill myself on a daily basis is starting to get to me.