I think that the use of the word sissy tends to reflect the guilt we feel about being girl-like. We're brought up to believe that it's the worst thing we can be, and indeed, so bad that some may need to imagine that a woman take the responsibility for our desires (forced feminization fantasies) or castigate us for wanting to be feminine, by referring to us in a demeaning term such as 'sissy'. I went through this stage when I was in adolescence, wishing my older sister and/or her friends, or a girl at school, would somehow discover that I was crossdressing and punish me by having me dress up and do what she told me, or challenge me to dress up as a girl and then hide my male clothing so that I couldn't change back, then tease me about secretly wanting to be a girl and referring to me as a sissy. All because we feel guilty about something that we shouldn't have to. 100 years ago, women were made to feel guilty about wearing pants. We've progressed past that. Maybe someday we'll be able to dress pretty without being made fun of. But I probably won't live long enough to see it.