"Put your shoulders back and boobs out!!!!"
"Smile with all four cheeks" hated that one.
"Sit up straight, **** it! Or I'll duct tape a bat to your back!!" also hated that one.
"If you're not one with your horse, you'll be one with the ground."
"Always remember, the ground is harder than it is to sit the trot..."
I never understood that one really... Maybe because it made no grammatical sense...
"I was eight years old, and I've never forgotten her face when she told me about watching you ride. She told me she saw you, and your horse was dancing in the moonlight."
-- A.C. Crispin's "Sylvester"