My Belarusian friend said a such phrase: хуйбудешь, He said that it was a joke, but could you please explain what he meant?
On its own with no context, it sounds like a reaction to an earlier statement: "The hell you'll be!" (or possibly "The hell you will!"), but it could be something entirely different. For example, there's a phenomenon similar to shm-reduplication whereby a word's entire sequence of sounds before its stressed vowel is changed to хуй-, to express annoyed or even aggressive dismissal. It can also be used on its own with a word said by another speaker, e.g.
«Бинго!» — «Хуинго!» If that's the case here, though, it's rather hard to figure out what the original word was.
Proposing dick (хуй) often means negation or condemnation. But you friend wrote two words "хуй" (dick) and "будешь" (will) concatenated. So this he probably constructed new word in joke. Russian language is inflectional, i.e. we can construct and modify words from parts. So we can add profanity parts to other words to sound more brutal.