God Loves, Man Kills is part of the canon of classic X-Men stories. Making subtext text, the original graphic novel focussed specifically on the persecution of mutants by the non-superpowered human population, drawing explicit comparison to the struggle of real-world oppression on people because of their race, gender, or sexuality. Sometimes those comparisons got a little too explicit, specifically in regards to race. Because the young X-Man Kitty Pryde, when faced with a black man referring to her as a "mutie", responds in kind by calling him the n-word. When Phil, the gentleman in question, protests, she insists that calling someone a mutant is just as bad. Which...well, it isn't. Mutant is a scientific term that definitely applies to the X-Men, whilst what she said is demonstrably a racist slur. You could see where they were going, but having a white woman call a black man racist was pretty goofy, which is probably why this is a less remembered scene from an otherwise well-regarded story.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/