What would you consider the toughest bodyweight exercise?  Do you think it’s the push up?  Maybe you don’t have great upper body pushing strength, and you haven’t seen anything close to resembling a push up since grade school.  While you may think this it’s difficult, there are people out there who can do tens and tens in a row.  Maybe it’s the pull up?  There are people who work YEARS to get a pull up into their arsenal, and one they do, increases in repetitions are few and far between, harder to come by than a good Drake song.  But again, there are people who can pull off 20 REAL pull ups with a moderate effort.
     In my opinion, the toughest bodyweight exercise is… The pistol squat.  Not the one that you see in The Crossfit games or people’s hairy version of it.  I’m talking about a controlled pistol in BOTH directions.  Lowering yourself to the ground and driving up, both under control.  If you can master this exercise, absolute strength is in your future.  Most people don’t have the mobility to get into the pistol squat and then the ones that do aren’t strong enough to control it.  Get good at these, and everything else will work itself out.