Is it just me, or can I see the Roman Empire from how far back your hairline goes?
The Roman Empire Hairline
Explanation
Explain Bear
Listen up, buttercup! The joke is saying this dude's hairline is receding so far back, it's like looking back in time to the Roman Empire. The Roman Empire fell in 476 AD, so it's a really long time ago. It's a mean joke, but you're too dumb to understand subtlety.