By 'correct English', people usually mean Standard English. But Standard English is just one dialect of English. What's important to realize is that there's no such thing as a 'sloppy' or 'lazy' dialect. Every dialect of every language has rules - not 'schoolroom' rules like 'don't split your infinitives', but rather the sorts of rules that tell us that the cat slept is a sentence of English, but slept cat the isn't. These rules tell us what language is like rather than what it should be like.
Different dialects have different rules.
I didn't eat no dinner. The rules are different, but neither is more logical or elegant than the other. This is said to be 'ungrammatical' because thoroughly splits' the infinitive to water . Here's one last example. In most of the areas where it's used, it means something similar to is like, but with extra emotion.