weird fetish

My bf lately keeps asking me if he can poop on my chest !? I thought he was joking but he just confessed he really wants to as it turns him on ... I'm soooo grossed out , I'm 12 weeks pregnant and if I smell his shit I'm going to throw up !!!!! what would you do ? Would you try it for his sake just once ? he literally asks me once a day now and I'm so turned off . Sometimes when we have sex he mumbles "mmm yeah shit on your chest" like seriously !??! Am I in a twilight zone ??