HTGS stands for horny teenage girl syndrome. This syndrome usually settles for fangirls such as beliebers and directioners. If you have HTGS you constantly think about sexual fantasies with celebrites and also your regular school crush.
Gabbie: Have you seen Liam Payne. He's so sexy. The things I would do to him! ;)
Hannah: Totally but I really rather fuck Louis
Randy: You guys sooo have HTGS