Ok, So I found this cool article about Star Trek Into Darkness that looks into the science a bit.
Warning, there are some minor spoilers ahead if you haven't seen it.
In the film, the article discusses Khan's ability to crush skulls with his bare hands:
The cunning villain Khan Noonien Singh [...] betrays his temporary allies to exact revenge on an old foe. Grabbing the Admiral Marcus’ skull with his bare hands, Khan compresses it with his genetically engineered might until the skull fails catastrophically (which is a nice way of saying the head exploded like a pumpkin with a firecracker in it, thankfully off-screen).
So, they look at some data on various studies, particularly a study about bicycle helmet testing that tests the crush strength of the human skull:
“Catastrophic failure [of the unhelmeted skull] during testing… experiencing a maximum load of 520 pounds of force.”
They also found data of what the static push strength of the average male is:
Looking to NASA, the Air Force, and even to the MythBusters, all the data that I could find points to an average static push strength of a medium-sized white male of a little over 200 pounds of force (or nearly 1000 Newtons).
So, if 200 pounds of force is what arms can do, you'd guess that legs would be much stronger and this chart agrees:
To interpret, at a leg angle of 160 degrees (nearly straight), an 5th percentile male can put about 2400 Newtons of pressure on something. Using a converter, that translates to 540 lbs of force, which is definitely higher than the 520 max of the skulls in the test...
Plus, characters are generally shown stomping on the skulls, which is different than static push. Static push would imply that you set your foot on the skull and pushed down as hard as you can. Stomping adds acceleration (force= mass * acceleration, remember?), which would greatly increase the amount of force applied to the skull.
So, yes, these numbers make it seem like it should be possible... though it probably wouldn't be easy. If someone more science-minded wants to review this, I'll make adjustments if necessary.
Then again, this article says it's not possible at all (warning, Game of Thrones spoilers). And this article from Time (also GoT spoilers) says it is but there's data missing to be sure.
Oh, as an additional thing, don't forget that, while corpse bones don't rot, they do become brittle with age, so the 520 lbs of pressure is certainly the highest figure.