This is a reference to a friend of mine on campus.
He wants to show up wearing to our Graduation wearing the traditional gown, but instead of a mortarboard, he'd be wearing a hard hat, and carry a wrench, and randomly saying "I Solve Practical Problems" I joked that he should wear his mortarboard on top of the hard hat.
So here's a pic of Lisa wearing a (badly drawn) hard hat with her mortarboard on top.
Though to be honest, I don't know if I even want to go to my own graduation.