Can You Answer These What If Hypothetical Questions?

If the bullet just made a small hole in the fuselage (body of the aircraft) and exited, then there won't be much damage. This is because the cabin of theaircraft is pressurized, and the hole will only create a small leak, which wouldn't affect the pressure level of the cabin.

If the bullet hits a window

If the bullet hits a window and the impact is powerful enough to actually blow the window out, then you are in for trouble. Big trouble. As mentioned earlier, the airplane is pressurized. Although a small hole wouldn’t affect the pressure level significantly, when there is a (comparatively) large hole in the fuselage due to a missing window, then the pressure equilibrium will be disturbed. Due to this, all of the air inside the cabin will rush towards the missing window, carrying debris along with it. If the person sitting next to the missing window is not strapped in with their seatbelt, then in all probability, they will be sucked out.