Use humor as a push-pull tactic. Usually, I like to tell incredibly politically incorrect jokes (think Carlos Mencia) and I will have a group doubled over in laughter. Targeted humor works too. Once you have worked the group a few times and they accept your jokes, no matter how offensive they may be, catch them on it. Girls absolutely love cynical humor.
*Somebody says something stupid or outrageous and the mood is light
Me: Hey! LESS CRACK! That's what I prescribe for you! *Use your hands*
Group: *Cracks up even more, the butt of the joke is also in on it*
Me: *Stop for a second and say with a smile* You guys are horrible!
Me: But seriously man, jesus, did you just tweak out behind the shed over there and think that *blank* would be a good idea?
I use this routine all the time, and it works wonders. Most of the time, I will rotate through the group, making fun of everybody so that there is not even a trace of hostility, but instead a solidified connection. Of course, your humor needs to be congruent with your personality to have the best effect.
-Damian