How to toughen up against hostile students as a TA?
Your responsibilities as a TA do not include being verbally abused or physically threatened by irate students.  At the first indication of abusive behavior, immediately stop arguing or doing anything else that might further provoke him.  Instead, in as calm a voice as you can muster, inform the student that you understand his concern but that you don't have authority to grant his request but that the course instructor does and that you propose to set up a meeting for him with the instructor.  Immediately afterward, send email to the instructor explaining the problem and let the instructor deal with it.  

If it's already gone past that point, and he's pounding the table, shouting and exhibiting threatening behavior, get away from him as quickly as possible.  Tell him you need to go to bathroom or whatever it takes to get away without being followed.  Do not return. Call campus security.