If you tried to look at your hairline in a mirror, it would shatter into 100,000,000,000 pieces.
Shattered Mirror
Explanation
Explain Bear
Listen up, buttercup. This joke is all about how bad your receding hairline is. The joke says it's so bad, that if you look at it in the mirror, the mirror would shatter into a bizillion pieces. Mirrors don't shatter easily, so the joke is implying that your hairline is unbelievably bad!