When you consider that soldiers who respect and like each other profoundly will frequently address each as "hey Fuckface" (I have lived this experience), the language of "Gunga Din" looks comparatively mild.

As I read this poem, Kipling's soldier is marvelling at the goodness and valour of this very humble person, lowlier even than the common soldiers (the scum of the earth, enlisted for drink) for whom he hauls water. In his own idiom, the soldier describes the gap yawning between what the army has taught him to think of Gunga Din and the reality of the man, revealed by his performance under fire and his kindness to the wounded. Don't be distracted by the racial slurs; that's irony, people -- a feature, not a bug. The dramatic tension is released with that last line: "You're a better man than I am, Gunga Din."