Similar to a receding hairline; this is one that recedes so quickly it seems to be more noticeable with every passing moment, and can be likened to a brigade running away in battle. Most common in men in their twenties or early thirties.
"What's with Joe's haircut? It seems to be styled the same but it looks way different for some reason."
"I wouldn't mention it to him. He's trying to hide his retreating hairline."