How to block someone as thread admin?

Hello,
I do not know where to ask this nor can I find it myself.

If I start a thread, how do I block someone from posting there?

I guess the only way is to ignore that user? If so, what if I just want to ignore that user for that thread only, not throughout the forum?

https://www.forexfactory.com/userguide#forums-thread_starter_controls