How can you quietly gauge someone's level of tolerance for LGBT people? Talk to them about an LGBT movie/series.  As tasteless as this may be, but you could pretend to be homophobic and transphobic or at least sceptical of LGBTS. 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'.