My main superstition on the course is if someone says "Nice!" or "Nice Shot/Throw!".... it's going to hit a tree. Even if we are throwing at a basket in the middle of a wide open field, odds are that a tree will sprout up like a magic bean stalk and block the disc.
I "jokingly" tell my buddies to stop saying "Nice" because we play friendly casual rounds... but I give them the ol' stink eye on top of it so they know it's super cereal.