Coincidentally enough, I was walking out of Walmart as well and noticed a woman approaching the store entrance from the parking lot. Just before she got there, though, she smacked the palm of her hand against her forehead and muttered out loud, "Dammit...I forgot my mask." She did an about-face and started walking back to her car in the parking lot.
Funny thing is...she was already wearing a mask and it appeared as though she failed to notice that (kinda like the guy who's searching around for his glasses only to realize that they're sitting on top of his head).
I thought about following her to her car to see if she tore it apart looking for the mask that was already on her face, but took a pass. She'd already provided me with a good chuckle.