Did you talk to him?

Teachable moment right there. Next dead ball...have a brief, but definitive, conversation about his ability to remain impartial, or else give the seat to someone who can. I actually once had a mom admit she couldn't be impartial (sub-varsity game) so she had the coach get another parent to keep the book.

I don't think I would have waited, but I could see doing it either way. I agree, though, he and I are going to have a chat at some point soon, if not immediately.