¿Cómo Se Dice "Trollface" en Español?

While in Walmart this evening, I passed (perhaps foolishly) through the cookie aisle as I picked up a few things. In this aisle, I came upon a middle-aged Hispanic woman and her young child - maybe two or three years old. The child was pitching a fit over something - given the aisle I was in, I had a reasonable guess as to why - and his mother was trying to quiet him down. As I came towards them, the woman briefly locked eyes with me and then turned to her child and uttered a Spanish phrase that I had heard many times before in similar situations:

"Cállate o el gringo te va llevar."

"Be quiet or that white guy will take you away."

Apparently there is a superstition among certain segments of Hispanic culture that white guys ("gringos," to use the occasionally-derogatory colloquialism) will will steal away small children, usually to sell them, but the motive tends to vary by whim of the storyteller. In a way, the concept is similar to American culture's "boogeyman" or "Bloody Mary" (or if you're a South Park fan, Biggie Smalls), in that the kid's mind creates this ambiguous entity that will do them harm if they do or don't do certain things. Santa Claus fits the mold too, but so far as I'm aware, Jolly Old St Nick his never been accused of kidnapping naughty children; that would make for a great SyFy Channel Special, though.

In any case, I'd seen it before. Having spent two years living in Guatemala, I was made an occasional scapegoat and boogeyman in similar situations. I also came to be fluent in Spanish during that time, and that skill has served me well in many circumstances over the years. My accent has atrophied greatly due to lack of daily use, but my vocabulary and my comprehension are still decent, and my blonde hair and white skin give me great cover and a brilliant element of surprise, as few expect a "gringo" to be able to speak Spanish beyond "Where is the bathroom?" and "One more beer, please."

The little boy looked at me coming towards him and briefly stopped whining. His mom looked up at me at the same time, so I decided to break cover. As I passed by, I looked down at the kid and smiled at him.

"Házle caso a tu mama," I said in Spanish. ("Pay attention to your mom.")

The little boy's face became this:

Mom did this:

. . . and I walked away grinning like this: