In Poland, the April 1st custom is to soak people with water unexpectedly, rather than pull pranks. ;3

I didn't do it this year (because I'm assuming people would just get outraged), but when I was still with my family, I would do horrible things like stick an ice cube in my sister's t-shirt to wake her up and pretend to spill 'hot boiling' water over people (it wasn't actually hot!).