How is rude, unprofessional behavior by one student toward another student handled in graduate school?
For what it's worth working in higher education I can guarantee the professors have noted the unprofessional behavior from the student(s). In project settings it's fairly evident who is completing the work. Often universities or the specific schools within them do have conduct guidelines which if they were violated can result in removal from the program. Unfortunately, in the world you're likely to encounter these individuals as well and should learn how to address such issues as they may even be in a higher position in your organization.

It really depends on your institution on the specific outcome but be prepared as you will encounter this again and typically the actions they exhibit are systemic of lack of repercussion.