Westbymidwest claims this is in the Mission District and we’re just going to have to take his word for it. (link)
It is. It is on the wall of the 99¢ Store at the corner of 18th and Mission, on the wall that faces 18th street. It’s farther down than one might notice, across the street from that tattoo parlor/bikini shop.
Actually, I just walked by there a few minutes ago: BUFFED!
The blog so nice they named it twice. (And to be clear, it's mostly about the Mission.)