Consider the actions of Sebastian with Feste, with Sir Andrew, and finally with Oilivia in Act IV, scene i of Twelfth Night.
"Are all the people mad?" (line 26) How does each character confuse and baffle Sebastian?
From the moment that Sebastian enters the play in Act III, scene iii, the audience has been waiting for just the comic misunderstandings that happen in Act IV, scene i. Sebastian and Viola are twins, and so it must be (a comic rule) that Sebastian will be mistaken for Viola in moments of extremity -- Andrew having intended to duel Viola (Cesario) to the death over Olivia, and Olivia head-over-heels in love with Viola (Cesario). So, in effect, not only are Sebastian and Viola twins, but Viola is pretending to be a guy named Cesario. Wheee! Comic complications galore!
Sebastian's first confusion involves Feste (or simply Clown) at the top of scene i. Feste is insisting that Sebastian is Cesario (really Viola) and that Olivia has sent him to fetch Cesario and bring "him" to her. Obviously, Feste confuses Sebastian for Viola. Sebastian treats Feste as if he is a crazy person who has randomly accosted him on the street, and after trying to simply tell him to get lost, he gives him money. Sebastian says:
I prithee, foolish Greek, depart from me.
There's money for thee: if you tarry longer,
I shall give thee worse payment.
Apparently, Sebastian, unlike his sister, is not afraid of a good fight.
Which leads us to the next hapless character to encounter him, Andrew. The last we saw Andrew he matched Viola in cowardice and was unable to follow through on his duel against her. Now the audience will get the violent payoff that they have been waiting for, as Sebastian vents his agitation against Feste on Andrew. Andrew touches off Sebastian's violent side by striking him and saying, "Now sir, have I met you again? There's for you!" While we can well imagine that the cowardly Andrew merely taps Sebastian, Sebastian responds by beating Andrew to a pulp, adding, "Are all the people mad?"
Sir Toby must pull Sebastian off of Andrew, and when Toby claims that he will bring Sebastian to the authorities, Sebastian draws his sword on the lot of them (by this time he faces Feste, Andrew, Toby and Fabian). Toby, not to be outfaced, draws in response.
At this moment Olivia enters. She throws herself in front of Sebastian, whom she must defend out of love, believing him to be Viola (Cesario). She chides Toby and shoos everyone, save Sebastian, offstage.
Here the tone of the scene does a complete 180 degree turn. Olivia woos Sebastian with her unconcealed affection, and he suddenly finds himself falling in love at first sight with Olivia, apparently forgetting, at the drop of a hat, all the early strife of the scene. He follows Olivia off in a lovesick swoon. He says:
What relish is this? How runs the stream?
Or I am mad, or else this is a dream.
Let fancy still my sense in Lethe steep,
If it be thus to dream, still let me sleep!
And so, as eager as he was to escape the mad dream in the opening of the scene, here he is more than happy to sleep and dream, if it means that Olivia will be with him.