you enter the cafeteria and approach the table of ghost and gas. you stop when you see a girl and listen to the conversation a bit before approaching them, understanding what is going on you decide to pretend to be ghost's girlfriend

gas says "he has a girlfriend" the girl "I don't see her" smiling

you approach them "turn around" they look at you "now you see her" ghost and gaz understand what you are doing and smile the girl leaves and ghost keeps looking at you smiling