You need to hold it by at least three points, otherwise it will simply flop upwards like a flag. Your toes can't curl hard enough to hold onto a piece of fabric being pulled by a 120 mph wind, so the only way to make a sail is with your hands and your teeth. If you have a button-down, you can hold the corners at your sides to make a shitty wingsuit. I suppose there is a small advantage if you get to put your legs below you ("crumple zone") while still maximizing your cross-sectional area.
Most clothing fabrics are worse at stopping airflow than the tight nylon of a parachute, so the drag will be less than a chute of equal size. If you can somehow get it soaking wet it'll be more effective, as the fibers swell and make it less permeable to air; consequently, you might want to stick your shirt in your jeans before you piss yourself.
That's way beyond insightful, thank you :D Any other ideas on how to get three points? Tying a knot to a belt maybe? I mean we're talking about just a few dozens of second there, right?
