The whole point of slang is that it isn't proper speak. Merci, but if you want to sound like an idiot that can't pronounce a simple French word like "beaucoup", then be my guest. Also, I made the remark about being southern,
because I've
only ever heard it mispronounced like that down here in the "sowth", and when I looked it up, it listed that it was slang in the south-east US. Hence, he's probably southern. I actually had a friend say that to me once, and I gave him a puzzled look while saying, "Wait... you mean 'beaucoup'?" "Yeah, boo-coo!" "..."
So, untwist your panties, suthnur.
EDIT:
I mean fuck... even the Vietnamese guy in Full Metal Jacket can pronounce it properly:
http://www.youtube.com/watch?v=gyGOJ1_kcI8#t=1m28s