when you see a really pretty, beautiful and hot girl or boy and you try to talk to them, but after they open their mouth, you run away. It's either the smell, awful teeth or just crazy low man voice (for a woman) that scares the shit out of you and makes the illusion of pretty face disappear forever.
A: hey look at that girl, ain't she hooooott?
B: go talk to her!
THE GIRL: MOOOO
A: omg no her teeth look like they belong to a cow
A: hey look at that boy, ain't he hooooott?
B: go talk to him!
THE BOY: Hey, how are you?
A: omg no, i could smell all the garbage in the world from his mouth. Let's just get out of here. He's a real mouthllusion.