Well if your son allowed someone to smoke pot in his room and he broke a rule that gets him kicked out then he deals with the consequences because he allowed it. It’s like serving a minor, you broke the rule. The responsibility of not having drugs in the room in on the person who signed the agreement. And seriously, if your son allowed his room to smell of pot so much that he got an RA called in him I just don’t believe he wasn’t getting high too, just because when he was a kid he didn’t like it doesn’t mean at 22 he wasn’t doing it but it doesn’t matter, he would be in trouble for it regardless.