Provided the "personal reasons" the customer thinks is the cause for closing the account are not predicated on any prohibited basis, you don't owe the customer any explanation beyond your right to terminate the account/relationship (per the standard "canned" disclosure language).
We reserve the right to close an account/relationship at any time, with sufficient notice. We are exercising that right.
If you believe the customer could become violent/present a danger to bank employees/other customers, consult with legal counsel (trespassing, restraining order, etc.)
"Remember no man is a failure who has friends." - Clarence (the Angel) Oddbody - It's a Wonderful Life