LIBBY: The two minutes you are standing on those stairs tonight will determine the social status for the rest of your life.
RORY: Wow, what if you trip? I mean, not that you would. You wouldn’t. I might. Probably will, actually. Could be a real Cirque du Soleil kind of night.
Cirque de Soleil (“Circus of the Sun”) is a Montreal-based entertainment group, and the largest modern circus in the world. Founded in 1984 by former street-performers Guy Laliberté and Gilles Ste-Croix, it is known for its spectacular theme-based performances, and has won many awards.
Rory is presumably thinking of acrobats and tumblers when she talks about tripping on the stairs as a Cirque de Soleil moment. This is another of many circus references in the show.