You gonna slice them up real nice? (referring to cut up tomatoes)
Is it grammatically right to use the word nice? Should it be an adverb? Such as:
You gonna slice them up real nicely?
Which is right? Or are both right?
Since the sentence starts with "you gonna," it is impossible to read it as a formal written English sentence. In spoken language in America, "nice" goes here and never "nicely."
However, in formal written language, the context probably calls for an adverb (I am told that even in informal language, adverbs are used here in Britain, but Friends is set in the US.) So I might write "She sliced them very nicely." (Using "real" for "very" is also informal.)
I like how the answer by hunter points out that this is a sitcom script. If all the characters spoke in perfectly grammatical sentences, the language might sound stilted, and therefore unrealistic.
I'd also like to point out that nicely might not even be the right word to use; it depends on if the speaker is modifying the verb slice, or the noun tomatoes. In other words, the question could be asking, in essence:
Are you going to slice them up so that the slices come out nice and even?
Will the cut tomatoes have nice, even slices?