I wrote a letter to the editor of the American Journal of Physical Anthropology attempting to debunk the common misconception that primates show their canines to advertise aggressive intentions (i.e., I'm going to bite you). For most monkeys and apes, canine exposure is actually a peaceful signal, much like the human smile. Here's a link to the letter (subscription required).
UPDATE 6/8/12: You can now download a postprint version of this article here. And if you don't believe me check out this article from Current Anthropology by Samson and Waller (2010).