Fraternize

Fraternize, according to the AHD means:

1. to associate with others in a brotherly or congenial way
2. to associate on friendly terms with an enemy or opposing group, often in violation of discipline or orders

The word ultimately comes from the Latin fraternus meaning "brotherly", which is a form of the Latin word frater meaning "brother". I found it's Latin origins interesting in comparison with its modern usage. Looking at the Latin from which it comes, I would assume that to fraternize is a good thing, like the first meaning of the AHD suggests. The word suggests brotherly love and friendship, but the way I most often hear it used is following the second definition, where the fraternization is not good because it is being associated with someone who is not supposed to be given a friendly attitude. I think it's interesting how a word that initially is a good thing can pick up such negative connotations. To me, I'll always use the first meaning because I think that "associating on friendly terms" or "in a brotherly or congenial way" should never be used with such a negative connotation because it just widens a rift in humanity.

-American Heritage Dictionary