I'm happy to be described as heterosexual in circumstances where that is relevant to the matter under discussion . I don't like the word 'straight' As what's the opposite? Crooked? Bent? If we're talking about gay marriage, the sexual orientation of a person may well be pertinent to the discussion ( if the person wants to mention it). There are many situations where descriptions other than 'human' are appropriate. Sometimes I would want to identify myself as a woman, as white, as a mother, as a grandmother etc