December 28th is "Day of the Innocents" in Mexico. It's a day for practical jokes, similar to April Fool's Day (April 1) in the US. "Day of the Innocents" commemorates the day that little boys were slain by King Herod in an attempt to to assassinate baby Jesus (and so King Herod was tricked? or because the children were innocent? I'm not entirely sure...). If someone falls for the joke, the standard line is "Inocente palomita que te dejaste engañar" (innocent little dove, you let yourself be fooled).
I somehow completely missed the memo that this holiday existed (though in my defense, I had either been in the US or traveling the last 2 years on the 28th) until this year when I completely fell for a joke on Facebook (thanks Cindy and Carlos!). So.... now you (and I) know!