Retard.
Just throwing this out there- I recently saw somebody on my friends list set their status as 'retards tilt me'.
While I know that the language filter on League is pretty decent when it comes to statuses (and the chat one, if you choose to use that- I don't) I don't understand why this word is available. Retard, retards, retarded, retarding- these are all valid words that can be used in non-discriminatory contexts. You could technically say that if somebody had a dying need to speak of retarding force in League of Legends chat, it being blocked may hinder them. But let's be real. The average League of Legends player that would use the word retard would only use it in a offensive manner.
So block it. Count it in with all the other offensive words. I can't even fathom why I need to bring this up. Please note, this isn't a place to discuss whether the word 'retard' is appropriate to use or not- this is the twenty first century. It isn't. Come on.