What forces act on an airplane's door from the outside in cruise?
A door that is, say, 36" x 80" (0.9m x 2m), with a surface area of 2880 sq/in (1.8m2), at 8 psi (55kPa) max cabin pressure differential, which most airliners run at, will have roughly 12 tons (102kN) acting on the perimeter fittings trying to blow it out. Any other forces acting on it are microscopic in comparison.  

For non plug type doors that depend on bayonet latch pins, the shear loads on the pins are such that it is impossible to move the latching mechanism.  If superman was able to move the operating lever, it may or may not just bend the linkage, but no human will be able to move it.

For a plug door of the dimensions above, it has to move inboard to start to open it, so you would have to be able to apply 12 tons of pull force to unplug it.

Just the acrylic cabin windows are holding back over half a ton each when you are cruising along at 38000 ft.

This is why you don't have to worry about a crazy person trying to open a window escape hatch in flight.