The unfortunate result that occurs after incest, sexual harassment, or intimate relationships are ended between closely-related family members, destroying all holiday spirit, hence the name Thanksgiving Syndrome, because of the dread of seeing that special someone at the dinner table again for the holidays, which would inevitably relive the once pleasureable or even forced orgasms that secretly occurred with that someone.
John: Why does your sister look so depressed when tomorrow is Christmas?
Mark: She has the Thanksgiving Syndrome.
John: The what?
Mark: Our cousin fucking raped her last month, and the unconvicted son of a bitch is going to be at our Christmas dinner tomorrow.