Sheep shagging's definitely not common over here. Not while they have yer mamma...

There is currently a commercial for K-Mart based on this type of piss-taking. Most of the lines start out "Yo mamma is so thrifty..." and the big "Oh no, she didn't" line is "Yo mamma's so fiscally responsible, she..." I'd say if a commercial like that works for a common US audience, the dozens aren't that big a secret.

I think in my case, it's the Air Force's fault for putting people from a whole bunch of different ethnic groups and cultures together. It started as a Black thing, but has spread.