Satire refers to the criticism of mannerisms and social behavior of specific groups using wit as a conduit of commentary. In other words, satire is a parody of something or someone (as well as a situation), but instead of it being openly criticized and talked about, the commentary is sarcastic, ironic, and subtle. Only those who are "in it" can tell the difference between something serious and something satirical.
The Importance of Being Earnest is rife with these very instances of sarcasm and irony based on the satire that Wilde creates of the very imperious English upper classes.
An instance of satire that stands out in Act 2 is the entrance of Algernon posing as bad brother Ernest in Jack's manor house, and his eventual meeting with Cecily. This is satirical in that Wilde is using two extremely shallow, clueless and seemingly careless people to represent the ideal melodramatic romance. Rather than presenting a damsel in distress being rescued by a courageous knight-like lover, we find the dyad made of Algernon and Cecily as two clueless youths without a very strong grip on reality.
For once, Cecily shows Algernon (whom she believes is Ernest) her personal diary shortly after meetiing him. What is truly satirical about this is that, in that diary, Cecily has already mapped out from beginning to end the daily goings of her imaginary relationship with Ernest even before she actually meets him. Moreover, Cecily finds it rude that Ernest (Algernon) does not remember some of the things that "took place" between them. Surely, since she invented the relationship it is impossible for Algernon to remember anything in a diary he has never read. However, this ridiculous dialogue and the asinine nature of the situation makes the entire thing so bizarre that it produces the comedy of it.
On his part, Algernon also follows along with Cecily's nonsensical rant and claims to be truly in love with her at first sight. He sees that Cecily has a weird obsession with the name Ernest, and when he asks her what she feels about the name "Algernon" he is told that
CECILY:But I don't like the name of Algernon.So here we have a good example of a joke made at the expense of something serious: The satire is made on marriage and courtship in order to expose the shallow and plastic nature of it in this type of society.
ALGERNON:Well, my own dear, sweet, loving little darling, I really can't see why you should object to the name of Algernon. It is not at all a bad name. In fact, it is rather an aristocratic name. Half of the chaps who get into the Bankruptcy Court are called Algernon. But seriously, Cecily…[Moving to her]…if my name was Algy, couldn't you love me?
CECILY:[Rising.] I might respect you, Ernest, I might admire your character, but I fear that I should not be able to give you my undivided attention.