fuck ufck fcuk cfuk ucfk cufk fukc ufkc fkuc kfuc ukfc kufc fcku cfku fkcu kfcu ckfu kcfu uckf cukf ukcf kucf ckuf kcuf
Note: these 'words' (valid or invalid) are all the permutations of the word fuck. These words are obtained by scrambling the letters in fuck.