Thanks for reportig this issue, and sorry that you had to go through this.
Any kind of threat is of course unacceptable. I assume it happened in the second of the games you played togother, can you confirm this (that makes it easy to confirm what happened). I assume a ban will happen (I can't do it myself, I pass this on).
In the meantime, to make sure you are not paired with that player again, blacklist them, if you haven't done yet (go to the "Friend list" tab, then switch to your black list and enter their user name).