I wish he’d grow ape hair.
Explanation: This joke uses a play on words involving “ape hair” and the phrase “grow a pair,” which colloquially means to become more courageous or assertive, often in reference to masculinity. The punchline, “I wish he’d grow ape hair,” humorously implies that instead of shaving, the brother should grow back his body hair, which indirectly suggests he should also become braver or more assertive. The humor arises from the clever double meaning and the playful twist on the expectation of body hair.