Can someone be banned from Y!A for being a jerk?

First of all, the answer to that is yes. You should report them for inflammatory overtones. Remember Answers attracts users from all walks of life and offensive content against every group is strictly prohibited under the Community Guidelines. By reporting the flame-baiters, they will be put on notice their inflammatory comments won't ever be tolerated by the rest of this community. It would be best if they took their comments somewhere else where it's permitted.

Second, in order for users to get their accounts suspended, they have to either incur a few TOS violations or a historical pattern of misuse. A suspension can also result when user get too many violations in rapid succession. When users get repeatedly reported, their accounts get reviewed and subsequently suspended if the staffers found they have caused more than enough problems here.

They used to be flagged so that when they opened a new account they would be suspended BUT as has been shown recently that no longer happens so users that are known for being disruptive paranoid, delusional and harassing and ranting about other users in their answers and by email are now back and did not learn anything at all since they are still at the things they got suspended for.

You can try emailing the team about them but going by the return of someone who was banned being back it may not help.