If you know or care at all about punk music, feminism, activism, or social justice, you probably know that seminal Riot Grrrl Kathleen Hanna is nothing short of a force of nature. And if you know and care about all of this, you were probably sitting near me at the Wilbur last week, eagerly awaiting the Bikini Kill frontwoman’s talk, “My Art: Punk Rock Feminism and Beyond.” But if you weren’t, or you don’t, or you’re wondering why the hell Marty Walsh declared April 9th Riot Grrrl Day in Boston in Hanna’s honor, then this one’s for you.