what's up, dawg

so yesterday after the movie, I was getting a little hungry so I decided to stop by mcdonalds and grab a snack. as the guy was handing me the food he says, "thanks, dawg". yes, someone in a place of business while still on duty said "thanks, dawg". now this got me to thinking when did "what's up, dawg?" become an acceptable way of greeting people? no "how're you doing?" or even "what's happenin'?" now the only way that I can think of that being called a dawg would be beneficial is that by calling you a dawg, the person calling you dawg implies that you're one of the group or pack 'cause I've looked at my dog and he's pretty stupid and lazy but he's cute as hell so unless the drive-through guy was hitting on me, the first explanation will be the one I'm sticking with until someone can convince me otherwise.