As always when discussing the usage of English words, it's pleasing to look at Webster's 1913 dictionary, which helpfully includes this definition of "tool":
reply> A person used as an instrument by another person; -- a word of reproach; as, men of intrigue have their tools, by whose agency they accomplish their purposes.
Okay but how is it used in society? I don’t know many people who refer to Websters. Notice your Webster’s doesn’t include the insult usage.
replyI see your Websters and raise you Urban Dictionary:
> That guy who makes us shake our head in disbelief but at the same time makes us feel better about ourselves since we are not him.
Please consider social and modern day usage as well when discussing English words.
Also 1913? Wow.