In the last scene of Hamlet, how does Hamlet use "antic disposition" to create humour?

Only one question per submission,
please.

It is important to note, before answering your question,
that "antic disposition" is a term that Hamlet uses in Act I to describe the way he intends to
behave (crazy) while he prepares to revenge his father's death.  When he returns from England in
Act V, there is really no more sign that he is acting crazy, yet he does find humor in some of
the situations in the final scene of the play.

The final scene of
Hamlet, Act V, scene ii, actually involves a few different, "scenes," if we
think of a scene as a unit of action that begins when characters enter and ends when they exit. 
Not all of these mini "scenes" necessarily contain humor.

First is
the interaction between Hamlet and Horatio, where Hamlet describes how Rosencrantz and
Guildenstern were substituted for him, and went to their death in his place.  Though Hamlet
always has opportunity to be played as a witty, intelligent man, there is no overt sign of humor
in this portion of the scene.

Upon Osric's entrance we have a "new"
unit of action.  Osric is as much a clown as the Gravedigger, a foppish courtier with whom Hamlet
has a bit of fun.  This interaction could be seen as Hamlet putting on an "antic disposition,"
but his behaviour is not so much "mad" as it is satirical.  He is making fun of all the protocol
and pomp and circumstance of behaviour required at court.  Most of the humor revolves around
Osric's hat and whether he should wear it or not.  Hamlet insists that he wear the hat, but Osric
protests, yet cannot (because Hamlet is the Prince) actually contradict
him.

When Osric exits, the tone of the scene changes again, as
Horatio says he is sure that Hamlet "will lose" in the bout with Laertes.  Hamlet grows quite
philosophical and speaks about "the readiness" being "all."  No discernable humor here,
either.

Finally, the scene culminates in the fencing match between
Hamlet and Laertes.  Many actors (including Mel Gibson in the Franco Zeffirelli movie of the
play) bring a sense of the "antic" to this part of the scene, though there is nothing in the
lines to indicate that it should (or should not) be played this
way.

So, apart from the overt humor in the interaction with the
foppish courtier Osric, the playing of the tone of the scene is really a decision for the actor
playing Hamlet.  There are as many takes on Hamlet's disposition as there are actors to play the
role.

For more on humor in Act V, scene ii, please follow the links
below.