Spoileruring one movie (forget which one), this little kid, probably about six or seven, was sitting right next to me yapping away at his mom. The mother didn't tell him to keep quiet, so I leaned over to him and whispered (carefully, so the mom wouldn't hear), "Shut the f*ck up or I'm going to carve out your liver with a dull spoon." Since the kid was so young, I had plausible deniability, but he didn't say anything anyway. It did get him to keep quiet, though
And no, this is not a joke.