There is one thing that seems to be absolutely non-existant on the English speaking forums/interwebz - the "twoja stara" pictures. This is a slang term meaning "your mom" (technically, "your old one"; there is also "twoj stary" - "your old one/dad"), connected with some sort of weird picture.
Like LOLcats - are pictures of cats with silly subtitles; the Polish kids enjoy (or enjoyed, as recently it got less popular) making "twoja stara" pictures.
It all begun with "twoja stara zjada meble" (your mom eats furniture) picture:
and "twoja stara pierze w rzece" (your mom does the laundry in the river)
This are completely stupid, offensive, but somehow childsish remarks, obviosly created by kids in primary school (please note that they are ultra offensive!!! gówniarze are the worst kind of human beings after all ;-) )
After this a LOOOOOOOT of pictures were made, with such pearls like:
"your dad has bread on his face" (idiom, meaning "your dad is red on his face")
"your dad has hijacked a plane"
and whole websites dedicated to it (just type twoja stara in google):
(I cant find "twoj stary sieje groze", it was great)
Onanizować się (tylko u faceta).
Onanizować się, inaczej: kłębić starostę, bić pięciu na jednego, marszczyć albatrosa lub freda, wkurwiać jelonka, drażnić druida, jeździć na ręcznym, skrobać lub strugać marchewkę lub pałę.
edit: the website thinks that Im a bot, so you will have to copy the links