Aliens would take your order and visit the tables. The place closed a few years ago, but here are some pictures of what it looked like...
https://www.google.com/search?q=mars+2112&newwindow=1&source=lnms&tbm=isch&sa=X&ved=0ahUKEwis5b7N4Z3dAhVH6oMKHbL_BgsQ_AUICigB&biw=1019&bih=465
They had great space-themed drinks too. And a space ship ride to get into the place. The inside reminded me of Total Recall. :-)