Despite what you may have heard from your local meteorologist, rain can be a boon in summer and having your own backup rain date plan can ensure that, however disrupted by the weather, you can still have a great day. My favorite rain date activity is indulging in personal pampering at my local barber. This experience not only refreshes and revitalizes me but also carries a sentimental value—the memory of my first Manhattan haircut with a hot towel shave from Kyriacos Demetriou, whose barbershop was just around the corner and whom The New York Times, in his glorious 1999 obituary,…