Stiles does Pilates while Derek's at the gym
I see your headcanon and raise you: Stiles teaches yoga while Derek’s at the gym and Derek gets so distracted by his downward dog, looking through the glass that separates the yoga class from the cardio room, he falls off the treadmill.
Erica can’t stop laughing for days. She also has it recorded, as she had been videoing Derek watching Stiles at the time to prove to him what a creeper he is:
“Why is it when Stilinski is taking his class, you always want to be on the treadmill? You don’t even like the treadmill, Derek.”
“If you don’t stop talking, I’m going to stop liking you.”
“Oh my god, you are so far gone on him his lame ass comebacks are already starting to rub off on you! How is this my life?” (she probably asks, eating popcorn….which she bought on the way over there, full well knowing she was going to get a show.
Plus, it’s not like she goes to the gym to exercise. She only goes to watch Derek drool over Stiles and flirt with the gorgeous new manager, Boyd).