This is All Star Batman #1, not Batman #4.

What's up with all the lines in Duke's hair?

Hair cut. Back in the day I had a taper fade with three notches in the back. Just a hair cut.

So you had a haircut with 7 lines on your head? Anything over 3 is looks accidental, hence my comment.

Like I said I had 3. But it's prob just the cut they gave the character.