If he said "Fuck you Negrito" that's obviously in a bad light as it's a direct insult.
Now, what if he said something along the lines of "What's the problem negrito? Have troubling keeping up with me?"
That I think can be split down the middle. Someone from North America for example would take it as "Whats the problem NIGGER? Having trouble keeping up with me? ... in South America, someone would just see it as a taunt, which happens all the time in professional sports. So, it all depends on the context, as well, as you mentioned, culturally relative.
Edit: I have no problem with a player lashing back at fans as long as it isn't physical violence. Remember that goal Adebayor scored against Arsenal, and he ran to the other side of the field just to taunt them? Well, I didn't see anything wrong with that. LOL. The FA did on the other hand, no? Didn't he receive a fine or a suspension?