Ouch. Yes, I've done this. Except that I didn't land on my top tube, since my bike is too small for me because I'm 6'5" and they're all too small for me. Oh, the usefulness of riding with a really long jacked-up seatpost and stem... the top tube is lower.
Still, one time when I first built up the bike I was riding with Onza clipless mtb pedals (remember them? and quiver...) and both feet unclipped at once... and my nuts hit the top tube, even though it was a ways down there. Luckily no one was there to see. Unluckily, no one was there to give me CPR...
With Look pedals, I've never done this, except when my pedal retaining mechanism broke and my foot popped out while sprinting away from a stoplight. But my other foot stayed in, and I maintained at least a 2" gap between my nuts and the top tube.