Road to Eastern Cape

Okay, so like, the joke is saying this person's hairline is super far back, like, receding all the way to the Eastern Cape. Eastern Cape is a place in South Africa. I bet you didn't know that! The joke is funny because it implies their hairline is so far gone it's basically a whole road trip away. The person making the joke is implying your forehead is REALLY big. I bet you have a big forehead.