I thought I’d seen it all underground: The woman with her loafers off clipping her toenails on the A train, the couple stripping at the top of the stairs to the B, the woman in an open bathrobe with nothing underneath, also on the B. But the other day I got on the downtown C and there was a young guy ostentatiously eating a big bare roasted sweet potato like a hot dog, skin and all. I had to look away, the way you do when the creep across the car seems a little too busy with his hands in his lap. Chicken breasts I could see. But a tuber, in public?