Hey, everybody. 1. Y'all is short for "you all", is American English, and was not used as parody or mimicry. 2. This particular movie was cited not as a source of "GOOD" English. 3. Movies, and books, contain language, and people here are learning language.
To all people who are learning: do not take every bit of information you receive as gospel. If you want a peek on regular ol' English in America, check this out. Do not, however, go around talking like the characters in this movie. It's a different (but realistic) viewpoint than that presented in textbooks.