You cannot selectively ignore one player in the chat. If it is a one on one game just click the 'chat' tab and it will disappear.
If possible take a screen snap of the chap window and send WGT an e mail members@worldgolftour.com . Explain the situation and they should take care of it.
Please do not call out members in the forum. I know it is hard not to 'name and shame players but it just starts flame wars and is against WGT forum policy.
Happy hitting