English translation for "廢"?
废 is a slang, and as NS.X mentioned, "waste" is a pretty good translation, as in


  I'mma waste you


Nonetheless, IMHO, 废 doesn't necessarily mean waste. Other meanings include:


What you thought it is, "to cripple".
"To destroy (life, job, etc)", as in 


  我废了你（的人生）
  
  I'mma destroy your life