SETUP: Lie flat on the floor and weigh your feet down with some heavy dumbbells or a sturdy object. Get enough bend in your knees so that you can keep your feet flat throughout the entire rep.
REP: Lie back with a medicine ball (/DB/KB) at chest level then explode up until you’re sitting upright, pressing the weight diagonally.
TIP: Don’t panic if you can’t press straight up. Only those with very good shoulder mobility will be able to do this. A high diagonal press is great.