When you ask your brother where his hairline is, and he points where it's supposed to be, and you say, "I don't see one there."
Vanishing Hairline
Explanation
Explain Bear
Listen up, buttercup! The joke is that the dude's hairline is so far back (or nonexistent) that his sibling can't even see it! Based and hairless, just like your dating life, LOL!