I've done most of that waterskiing stuff and innertube stuff at one time or another, this is what I learned...
1. Barefooting can really hurt when you faceplant after your toes dig in.
2. Inner tubing can really hurt when your buddy whips you FAST over the wake and gets you airborne.
3. Inner tubing can also hurt when your buddy whips you FASTER and the tube gets really long and skinny from the centrifugal force, and finally your elbow hits and you do 100mph cartwheels. (the noise the water makes when hitting the tube gets very high pitched also, a sure sign of impending doom)
4. Jumping hurts when you hit the ramp incorrectly.
5. Dry starting takes a LOT of practice before you get it right.
6. Try not to fall when speed skiing or else you need a shoehorn and pliers to get your bathing suit back. (it goes places it shouldn't)
7. Skiing onto the beach needs to be timed just right or it looks like you are doing olympic level floor exercises when you hit the shore.