The irony of systemic injustice
Imagine the kind of irony it would take to be able to write "All men are created equal" while still literally owning slaves. That's essentially the irony of systemic injustice, and it's the center of MacKinnon's feminism, that injustice against women is rooted in assumptions about what gender is and what it implies. The irony is that people believe their understanding to be morally good or at least morally neutral, but actually, cultural assumptions can be disenfranchising and wrong, according to MacKinnon, so a true paradigm shift is necessary to expose the injustice wherever it is.
The irony of sexual harassment suits
One of the tangible examples provided in these lectures is to show the history of women's suits against their abusers in courts of law. This ironic exercise shows the true disparaging of women and shows one element of the injustice against them, that even recently women were treated as if their rights didn't matter as much as the rights of a man, even when the legislation said something else. This misalignment of the legal code to our interpretation of justice is jurisprudence and it's something MacKinnon is very well known for.
The irony of prejudice
Most people think that being evil means twirling your facial hair and conniving against innocent people, but actually the most common and (by far) the most powerful form of evil comes in the form blindly accepting the 'normal' assumptions about certain communities. This is called prejudice, and MacKinnon's entire goal is to make non-feminists aware of the deep injustice that has been tolerated by way of prejudice, both in racial terms, and in the inequality of the sexes.
The irony of the patriarchy
By observing the radical under-representation of women in the legal system and in other arenas of public life, MacKinnon draws attention to another difficult, ironic aspect of feminism, that most of the time, appealing for justice will mean appealing to a room of mostly men. This was especially true during the time these lectures were delivered. Even if the women get to say their piece, there won't be justice until women's voices count as real, valid political opinions.
The irony of the issue of pornography
One might expect a feminist to be somewhat supportive of a woman's right to earn money with her own body by sex work of some kind or another, but actually that angle of feminism was primarily developed by MacKinnon's opponents in feminism. MacKinnon shows the dark side of the industry instead, focusing on the fact that paying for sex is immoral and wrong, and that most women involved in sex work were coerced in some way, including her cited example, the star of the blockbuster 80's porno, Deep Throat, whose main star accused her boyfriend later of forcing her into making the film against her will through manipulation and even outright violence. This itself is ironic, to imagine that these women performing acts designed for sexual pleasure might actually be the victims of a kind of slavery.
