went to the movies today to see Rambo and it was pretty empty. When I bought my ticket I asked the girl "this isn't one of those violent movies is it" She then went it this spiel " well, actually it does have a fair bit of violence... blah blah"

I thought she would find the humor behind my comment but she kept talking with a serious face and I interrupted and said " ah, I was just joking" she gave me a dead pan look dumped my ticket in my hand.

An important lesson learned.
She might of been annoyed seeing some woman before me talked her ear off with pointless gibberish

Maybe your tone was off, and maybe you forgot to make eye contact and smile big at the end of your sentence. Maybe she was just too serious.
A better statement might have been "Is this movie rated R?" her: "yes" you: "Why its not like theres any violence or anything right?"(chuckle)
Its not really that funny either way, but if she was interested she would have laughed. I think in this case she was just in serious mode.