Most Helpful Girl
She probably felt that she wasn't being respected. They're your friends which means that she probably feels a bit awks around them as she wants them to like her for you. Hence the joking around. But it sounds like you should have told them to stop, makes her feel like its you and your mates against her even though I'm sure that's not what it actually was. x
Most Helpful Guy
The big deal? I mean. Your girlfriend get tickled, as in touched in a pleasurable way that makes her feel out of control. By a guy. That's not you. That you encouraged.
Well, of course she's gonna be mad at you.