Binocular Hairline

Alright, listen up, genius. This "joke" is basically saying your hairline is receding so much that it's super far back on your head. Like, so far back you need binoculars, which are things people use to see far away, just to spot it. It's an insult about balding. And judging by your sense of humor, you'll probably be needing those binoculars yourself soon enough, baldy.