Beards
The women's beards that are used as disguises are described as looking like "broiled cuttle-fish". Ironically, no man in the Assembly looks close enough to recognize this fact and believes them all to be women.
Power
The women are able to convince the Assembly to rule that women should be in power. Ironically, one of their statutes (beautiful people must sleep with ugly ones prior to being able to be with another beautiful person) causes the opposite effect of order as we see a drunken elderly woman demand a young man to sleep with her.
Blepyrus
Praxagora tells her husband Blepyrus of the new statues in the city. He agrees with them all. Ironically, he knows that he is an ugly man and it works in his favor to be with more women, and we see him with two on his arm at the end of the play.
Victory
We hear that the Assembly voted to put women in power over the men. What is ironic is that the Assembly didn't vote for this because it was what they agreed with, they voted for it because of the large number of "shoemakers" that were cheering on the orator during "his" speech. Thus, their vote was based upon going where the majority is in order to keep any of their power.
Being a Man
The women come together in order to prepare themselves as men before going to the Assembly. Ironically, they continue to forget to swear upon Apollo, whom the men of the city speak of instead of a goddess such as Demeter.