English translation for "廢"? For example, 


  我廢了你


It can roughly translate to "I'll waste/break/ruin you", but that doesn't sound too accurate.

What "廢" sounds like is kindof like "crippling" yet less severe than that.

From what I can tell, it sounds like extreme, violent damage yet nothing as permanent as crippling.
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