At the height of her evil psycho ultra-competitive mean girl persona at Chilton, Paris Geller only has one weakness: Tristan DuGray. She'd had a thing for him for years, and he seems to be the only thing that could really distract her from being the best at basically everything. Tristan is out of the picture by season two and Paris moves on to far bigger and better things, but in the "Spring" revival episode Paris returns to Chilton for the same alumni event Rory attends and what do you know, there he is (even though he is NOT played by Chad Michael Murray in those two seconds of screentime). And she's just as rattled by seeing him as she is in high school. We later come to learn that this reaction is actually just exaggerated by her anxiety about her divorce from Doyle (boooooo) but it calls back to the days when even the great Paris Geller could be slayed by a crush.
