The fear of your crazy mother-in-law who think you are a horrible influence on her son/daughter (your wife/husband). You are especially motherinlawstrophobic when you are left ALONE with her.
Chris: Hey, Mrs. Calhoun. How are you doing tod-
Janet (mother-in-law): Don't talk to me! Your lucky you're allowed to LOOK at my daughter without me slapping you! You know that she almost married my best friend's brother's aunt's son-in-law? Yeah, he went to HARVARD. And where did you go? Community college? Whoop-dee-doo. Hooray for failure! You know she could divorce you whenever she wanted to! If you ever say ANYTHING rude to her, I told her she has permission to WALK OUT ON THIS MARRIAGE. Yeah, she can find a better man. Like the one that went to Harvard. Yeah, MR. HARVARD IS BETTER THAN YOU.
Chris: I HAVE MOTHERINLAWSTROPHOBIA!! GET AWAY FROM ME YOU INSANE, PSYCHO FREAK!
Marie: Hey Mrs. Henderson!
Katie (mother-in-law): Suck it.
Marie: *in whisper* Motherinlawsrophobia sucks.