One of the things I've learned of recently is so-called "groutfiti".

Urban dictionary provides an entry :

A form of graffiti. It involves writing in the tiny space of grout in between tiles in public toilets. The phrases always are made up of some pun using the word grout... This type of graffiti has no deep meaning, but it is a great example of intellectual fun.

A friend introduced me to this college campus pastime when explaining to me what a meme is.

Here's my contributions: