Don't watch a movie if you're going to pick it apart. "That wasn't realistic!" Movies aren't supposed to be realistic. They're supposed to be entertaining.
Look, some movies the 'facts' are so bad that it stops a movie from being entertaining.
A movie has got to be somewhat consistant. Okay, Bugs can plug elmer's gun with his finger, that is consistent with other stuff going on. Same with a truely over the top action flick like 'Smoken Aces', action equivalents of monty python or 'Another Scary Movie'
But when a movie that is trying to be otherwise relatively realistic, yes, it can be so bad that the movie stops being entertaining. For example, standard spy flick...its okay to never reload, be relatively unharmed by a grenade tossed close by, but to use a horse to chase down a motorcycle, unacceptable, to catch a bullet in your teeth and spit it back at the badguys, unacceptable.
Of course, there is a 3rd catagory of 'mistake' where real guns stand in for nonexistant ones. Take Die Hard, where bruce talks about the Glock 7, a ceramic gun that costs more than you make in a month and can get by airport metal detectors. Okay, there is no Glock 7. So it doesn't really matter that your Glock 19 is mostly plastic with a lot of metal. Okay, maybe the writer should have gone farther out on a limb with the name, like an "Elbonium 717 mark 2" but then you have the problem of gunners bitching 'hey that is obviously a glock!' Die Hard needed an 'undetectable gun' which is realistic enough, and needed to introduce it quicky. Another movie were Clint Eastwood is a Secret Service agent, they have the time to show the criminal make a resin gun, and then show the lethality of the gun, but that took like 10 minutes of movie time that could be spent on other things