The irony of the horses' desires
The play opens with an ironic scene of horses talking about how hot they are for their owners, and one of the horses tells the others about a new device that would facilitate that act. Obviously shocking, the irony is that the horses might want it. It's a joke, though, and it's meant to draw attention to the main issue with bestiality—it's essentially rape.
The irony of same sex attraction
It is not ironic that gay people would be characters in a story, but what is ironic is the way Lorca ties that theme together through most of the male characters in the play. It's something that everyone, or nearly everyone deals with, according to Lorca's play.
The irony of shock
Shock is the response to irony. In small doses, the effect can be comedic, but in larger doses, the reversal of expectation yields confusion and maybe even panic. The point of shock in the work is to exploit irony by showing people ideas that they would never expect, to stun them and make them reconsider their assumptions.
The irony of the play's fate in history
Of Lorca's plays, The Public holds a special place as especially insensitive and especially controversial, but ironically, we don't have the rest of it, so it's rarely performed, and it didn't see its first performance until the late 80's. That's a long time—almost 60 years. This also means that directors have liberty to write in more shocks and fill in the gaps, making for a very diverse, powerfully strange play.
The irony of social order.
Sexuality is not the only more (moh-ray) questioned in the play. Characters are often surprising and offensive, often misusing each other and lying. It's like a pastiche of the worse parts of society.
