Boyfriend wants to have sex with x mother in law

Hi all, I hope you will be able to give me some insight. My boyfriend of 7 years has had a couple of beers the other night and then proceeded to ask me if I could ask my X mother in law to have sex with him (she is way in her 70's). I was shocked but I know he had pics of much older women on his laptop as well. He is upset that I did not accepted that he only made a joke or that it was 'beer talk'. Most all our arguments are about other women. I know he has a keen eye for any other women. Am not sure how to handle this?

thanks guys!