My favorite is Fark's word-changing filters and their unintended side effects. The no-no words are scanned across whitespace and reversed, and any hits get translated to the approved word. "Shit" becomes "Shiat", the N word becomes "nubian", etc
Every so often someone will find their sentence that contains something like "I will have ham or egg in my sandwich" becomes "I will have ham onaibun my sandwich"
Every so often someone will find their sentence that contains something like "I will have ham or egg in my sandwich" becomes "I will have ham onaibun my sandwich"