Answer: No, I’m not being belligerent.
Step-by-step explanation:
That’s the sentence. In context, if you ask me to do something, and I say, “Why?” that is a full sentence. It means “Why should I do that?” but the “should I do that” is implied. And a technicality, the letter “Y” is functioning as a vowel in that sentence, as it sounds like a long “i.”