I may have posted this one before, but my considerable amusement of the moment is:
"Silence!"
The interjection, that is. As in, the thing somebody shouts when there's a ruckus going on, and everybody immediately hushes up. The reason I find it so amusing is that in fiction it's probably the most reliable command in the universe in terms of being obeyed in every conceivable setting, whereas in real life nobody ever, ever uses it.
These days you're likely to hear a tepid "Quiet, please!" or a needlessly self-aggrandizing "STFU!" but, oh, what I wouldn't give to see some imperious wag drop a proper S-bomb on an unruly gaggle of mooks and blatherskites!
Secondary Amusement: Firefox's dictionary doesn't recognize "blatherskites" and recommended "weatherstrips."