Why does my sister get repulsed and offended so easily?

All our lives, my big sister has been unpredictable when it comes to perverted humor and talk. Sometimes she's ok with it and other times she takes offense and distaste to it. It was a lot worse when we were kids and teenagers. She used to hate and freak out about everything explicit I liked talking about with my guy friends. She was repulsed with all my humor and my sexual instinct and told me no girls like things like that. To be honest, as a teenager I was surprised when I found out that all girls aren't like this. Some girls are actually more dirty-minded than I am.

We are adults now in our late 20s. We don't see each other much as we live in different cities. She's gotten a lot more lax about these things now that she's matured. But even now a crude joke can get her really irked. For example we played Mad Libs and she got bitchy about me piking works like: lubricant, penetrate, shaft, and many more that could be ambiguously sexual.

I know sometimes girls complain about male humor being too vulgar at times. I mean yeah, sometimes I don't like it either if the humor is so bad it crosses the line. Is getting offended easily a girl thing or a big sister thing?
Why does my sister get repulsed and offended so easily?
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