The McGurk effect tends to be minimized when you're interacting with familiar faces, but it gets worse if you're dealing with strangers. Things like the way the person is dressed or even what they're carrying can influence the words you think you hear them say. For instance, in one study, people confused the phrase "He's got your boot" with "He's gonna shoot" when viewing a staged video of a man chasing after a woman. This proved that you're more likely to hear (or believe you hear) someone say the word "boot" if they're carrying a boot, and you're more likely to hear (or believe you hear) someone say the word "shoot" if they're carrying a gun.
It's still not advisable to wave footwear threateningly at police officers.
But it's just "boot" for "shoot" -- who could possibly be affected by such a small misunderstanding? Other than, you know, people being tried for murder.
So basically, think of all your senses as the "yes men" to the CEO that is your eyes. Even when your ears are pretty sure your eyes are wrong, they're too timid to protest and will just go along with whatever your eyes dictate.
But that's not the only time your eyes screw you over ...