It was in the middle of a meal with other friends, so I explained my reasons and departed, I had to do that once too. It was very difficult as I was a guest in someone's home, but one of their other guests was holding forth with his bigotry and racism as we all sat in appalled silence. Eventually, with an apology to our host I got up to leave saying that I couldn't sit there and listen any longer without starting a huge argument and I considered leaving the table, and their house the least rude thing to do. I understand that the following morning, the racist was mortified at his behaviour, but he did not apologise and just blamed it on 'the drink', personally I think that excess alcohol reveals our true selves as the societal and behavioural controls are forgotten.