Ice cream man: Have a good afternoon!Each response is understood to represent a whole proposition/sentence, but in each case a slightly different part of the understood proposition is omitted:
BH: And you!
Me: You too!
BrE: And you [have a good afternoon].It struck me that BH's and my responses here followed in the pattern that we saw back in the discussion of me (n)either and nor I, with the Brit preferring a conjunction+pronoun and the American a pronoun + adverb. That's all I have to say about it really...that there's a pattern! Like most linguists, I love patterns.
AmE: You [have a good afternoon] too.