Hamlet:Hamlet Act 1, scene 5, 168–180
Here, as before, never, so help you mercy,
How strange or odd some'er I bear myself—
As I perchance hereafter shall think meet
To put an antic disposition on—
That you, at such times seeing me, never shall,
With arms encumb'red thus, or this headshake,
Or by pronouncing of some doubtful phrase,
As "Well, well, we know," or "We could, and if we would,"
Or "If we list to speak," or "There be, and if they might,"
Or such ambiguous giving out, to note
That you know aught of me—this do swear,
So grace and mercy at your most need help you.
We use "antic" as a synonym of "madcap," stressing deliberate playfulness. But for most of its history the word referred to grotesque and ludicrous qualities, especially in drama and pageants. With a sort of ironic understatement, Hamlet uses "antic" not to mean "madcap," exactly, but something closer to "mad"—bizarre, irrational, threatening.
How theatrical Hamlet's "antic disposition" will eventually prove is the subject of much debate. At times, it seems that the prince has stopped playing a part and has in fact become antic. Hamlet's performance will be all too plausible; but then again, he's been a student of the theater and is no mere amateur [see THE GLASS OF FASHION].
This scene comes at the end of Hamlet's first meeting with his father's ghost; he is swearing his friend Horatio and the officer Marcellus to secrecy about plans he hasn't really explained [see THERE ARE MORE THINGS IN HEAVEN AND EARTH, HORATIO]. Like the good actor he is, Hamlet plays out the coy gestures he'd have the two avoid—the kind of "ambiguous giving out" that would expose Hamlet's antic disposition as merely a clever charade.