Can anyone help me understand what's going on here?

I am 16, and I have a younger sister who's almost 13. We get along pretty well, but it's still a very "casual" relationship. I'm not too fond of the whole, "I-love-you-and-I'll-always-be-there" stuff.

Anyway, I recently got a job at a video game retail store, which, for lack of a better word, is a total sausagefest. I don't mind it, though. My co-workers are really great and incredibly funny.

So one day, I wasn't working, and my mom went to run errands in a different store in the same shopping center, so I took my sister and her friend to my place of work to wait for mom to be done. I was talking to my manager, who is somewhere in his 20's, and the third manager, who is 19.

We were just goofing around as we generally do, and this seemed to make my sister incredibly uncomfortable. She kept telling me, in a little "secret" language she uses, how she didn't like them and how they creeped her out.

Even after we left, she kept telling me at intervals all that day how she didn't like them, especially the 19-year-old. She also told me "They like you," but I really don't see it like that. I like them, too, they're really fun, but I don't see anyone as having a crush on me. However, apparently SHE sees it, and I "can't understand."

I asked my mom about this, because she was also a younger sister. She told me that seeing people who are interested in an older sister is a very disturbing event. I think it'd be the other way around, but I haven't had any problems yet.

Come to think of it, she was pretty suspicious of another guy friend of mine, but they got along better once he got a girlfriend.

Does anyone else have experience with this situation? How am I supposed to comfort my sister, or at least stop her from criticizing my co-workers every day? How can I help her deal with the threatening thought that her sister is a romantic/sexual being, even if there's no reason for her to worry right now?