Do it watching a girl rev up a car, matching the downstroke of the shoe you're jacking off with to the downstroke of her foot mashing on the pedal. Turn up your speakers REAL LOUD, and I bet you'll cum all over yourself!
Trust me, she knows. She caught me jacking off with those boots several years ago with the heel of a 7-inch platform pump up my ass. She had the pleasure of watching cum jet out my dick onto the wall behind me.