Yeah, you USA guys celebrate it in April 1 but today, here in Mexico (where the 83% of the population is Catholic) and the rest of Latin america and Spain (not sure but Wikipedia say so) celebrate "El dia de los Santos Inocentes" or Holy Innocents' Day in english.
Same stuff, everybody does pranks, I'm, honestly, not a fan of pranks and I'm not good doing them but anyway I/We have to be careful today, VERY careful. (C'me on even the news channels do pranks) The only good thing is that we're in vacation so I/We can avoid classmates' pranks.
Anyway be careful with Latin people, they know it maybe you don't, nah just kidding, but if they/you celebrate "Latin" traditions you know what to do.
Happy Holy Innocents' Day!!