Wolves and monkeys do that when expressing threat and dominance. But we use it to say "hi, I want to be your friend". Hmmm.

Reminds me of "interrogative greetings" : WHAT'S UP?! HOW YOU DOING??! WHAT'S GOING ON??!!

My vision of the future is a big, smiling, full-eye-contact WAZZZUP!!!! in your face, forever.