I hope that you can picture it. I wanted to whip out my camera phone, but a) I'd have to be so close that discretion wouldn't be possible, and b) I was a little afraid of him.
Starting from the top:
Long black trenchcoat
Black t-shirt (I think)
Pajama pants with orange and red flames
He was standing by himself in Walmart with his arms in front of him, hands clasped, like a body guard, just looking around - apparently guarding the bakery cookies. He stood there for probably 10 minutes, moved to the donut racks for a bit, and then disappeared.