The word "negro" can have pejorative connotations, as it may be associated with low class
status, ugliness, vulgar behaviour, noisiness, violence, dishonesty, sexual promiscuity etc.
In the River Plate region, for example, "los negros" is sometimes employed as a general
term for the lower classes and especially for lower-class people whose behaviour is
deemed vulgar and not "respectable".
 

Thus, the word can be employed with the intent to offend and to offend in racial terms;
often the word would be appended with further insult, as in the example "negro de
mierda" [shitty black].  

"Negro" can be used in the same way that other words referring to physical characteristics
are used as descriptors for particular individuals, eg "el flaco" [the thin one/beanpole] or
"el gordo" [the fat one/fatso]; these words can also be used without the article, eg "hola,
gordo" [hi, fatso] or "chau, flaco" [bye, beanpole]; thus, a group of friends waiting for
another friend might exclaim "mira, ahi viene el negro" [look, here comes the black
one/blackie].