If someone calls you a tool, how would you reply?

I am a business major. All of my friends have more liberal-artsy majors. One day, one of my friends quipped, ';Gosh, I think all business people are such tools.'; I got slightly offended since most of my family works in the business world but I said nothing, because frankly, I didn't know what to say. How do you reply to something like that? I mean, to me, the whole concept of being a tool in that sense is a joke considering every kind of profession is run like a business, where networking is key. Bureaucracy is practically universal in almost all professions. What I'm asking is, how should I reply if I don't want to offend?