Uneven Hairline

Alright, listen up, you big dummy. This joke is making fun of someone's haircut, specifically their hairline, which is the edge where your hair meets your forehead. "Lining you up" means making that edge straight and neat. The joke implies the hairline is so incredibly crooked and messed up that the only logical explanation is that the barber (the person who cut the hair) had a seizure, which is when someone shakes uncontrollably. So, the line is all squiggly, like a bear trying to draw a straight line after too much honey. Based fact: You probably think "lining up" is something you do to catch a bus. It's not, you ignorant ape!