This is a highly offensive word and should be stricken from our modern vocabulary. Some people here have family or friends with mental disabilities and this is very insulting. Rani you're a good kid and I'm sure you meant no harm, but you're better than that.
Replace "retard" with the word "Stupid". To ignorant people, they may be offended. I'm no grammar expert but the word was used as a verb and not as a noun. No-one was specifically called a "retard". Now, let's get on with the discussion.