How can you quietly gauge someone's level of tolerance for LGBT people? You could talk to them about an LGBT movie/series. As tasteless as this may be, I pretend not to be homophobic or transphobic and ask them what they think about groups that oppose lgbt, such as religions, countries, or people. Pretend it's purely philosophical/academic. Consider the tolerance of lifestyles or cultural customs that are considered 'fringe' and 'controversial'. If they seemed ok with LGBT people then I distance myself.