I review code frequently. When some of the code is bad, I manage to impress upon the writer that it's not up to scratch and why, and they produce better code to replace it and continue to produce better code in the future. Sometimes it's really fucked up code. Really bad.
Yet, incredibly, I don't have to use the word "fuck" at all. Amazing, I know. It's as if it's possible for someone to listen to criticism and improve their work without having to be screamed at. I have funny memories in which this happened to me as well; I wrote bad code, and then someone explained to me what was wrong with it, and then I wrote better code. Again, nobody said "fuck". Truly amazing.