Let's look at what an aircraft window withstands on a regular basis:
When an aircraft is flying at 35,000 ft, the pressure outside is 3.46 psia (psia is the absolute pressure, or the pressure above an absolute vacuum. Tire pressure is measured in psig, or gage pressure which is the pressure above the surrounding atmosphere.), while the pressure inside the aircraft is 10.9 psia. That leaves a differential pressure of 7.44 psi.
The Boeing 777 has windows that are 10.3 in by 15 in. This gives an area of 154 sq. in.
7.44 psi acting on 154 inches gives a net force of 1145 lbs. According to FAA regulations, the window has to be able to withstand a pressure at least 33% larger than that. That means the window can withstand at least another 378 lbs of force, and likely much, much more.
Because airplane windows are thicker in the middle than at the edge (this makes the outer surface of the window flush with the airplane exterior for aerodynamic reasons), the localized effect of a punch will be negligible. This means that one would have to generate in excess of 375 lbs of punching force to break a window, if the window were built to withstand the bare minimum required by the FAA.
But wait, there's more.
Aircraft windows are double-paned. The inner pane has a little hole at the bottom that equalizes the pressure on both sides of that inner pane so that only the outer pane is withstanding the pressure outlined above. The inner pane is approximately 3/8" thick (.375 inches) and made of stretched acrylic (stretched acrylic is regular acrylic that has been stretched to align the polymer molecules giving a greater longitudinal strength). Using some back-of-the-envelope math, this window pane can withstand approximately 4,900 lbs of force.
It is estimated that a boxer can punch with approximately 1,400 lbs of force. This is well over double what the average Joe can produce. A comparison of 1,400 lbs to 4,900 lbs shows that in a contest between an airplane window and a boxer's fist, the window wins every time.
There has been some question as to the validity of my calculations. I will be the first to say that I am not an expert in stress analysis. I also took a very simplified look at this problem because no lives depend on it and it was easier.
While my figures and calculations are likely not accurate, I found a paper (Page on Www.dtic.mil) describing a test that fairly adequately demonstrates airplane window strength. To summarize, an aircraft window withstood 1750 lbs of force with very little deflection, meaning, no, you can't *push* through a window on an airplane. And while the impact force of a punch is dynamically different than a push, I feel quite confident that you still couldn't punch through a window.
Also, the paper tested only one pane of a cabin window. If you were to take into account the second pane, the window definitely wins.