For erotic entertainment you can go to the Banana Bar in the middle of the red light district. They offer erotic entertainment but no sex. A lot of stag parties go there. You can also go to the erotic bar "La vie en proost " for lap dance and topless waitresses. And of cause it is fun to walk around in the red light district and do some window shopping.
A good place to eat with a group is Haesje Claes, 10 minutes walking from the red light district.