Driving with a passenger drinking

I am in a full fledged argument with a “friend”. First of all I live in WA. I have told him he cannot drink in my car. He continuously says per WA state law, if he drinks only he will get a citation and I will not. I disagree. The way I read the open container law is that the driver is responsible. I have been looking online and have seen both as responses to this question. I will not allow him to do this regardless, but am I crazy? It would be my fault as I am responsible for what happens in my car and a citation to me if he had a container in the car, right? Maybe both of us would get a citation, but I am quite sure I would.