I happened to be watching an account of "The Brady Bunch" and Florence Henderson commented on the fact that as soon as she kissed her co-star (can't remember his name) she knew he was gay.
I remember being sceptical that she could tell from a kiss while acting, but later they were interviewing Sherwood Schwartz, and he mentioned that after the first scene with a kiss, that Florence Henderson had come to him and said, "This guy's not Straight". I think she had a reputation as being pretty randy so she probably would have known.