Hahahaha no. We had 100k users/employees. And they were pre-created into the forum.
So we used the employee_id (One letter + 7 numbers like X1234567) as the username. People can remember employee_id of close colleagues (like your boss and team) but when you just want to mark:
Oh this topic is gold. Gonna mark Susan from the HR here.
You know her full name is Susan Summers, but there are 15+ Susans and 15+ Summers on the board.