Today I am ‘not a happy bunny’!
A ‘happy bunny’ means, a contented person. When used in the negative context referring to a person who is depressed or miserable. Not happy. Why? The Internet was down yet again. From last night until late this morning. Aaaagghhh! The luxuries of living on top of a mountain!
It’s not a phrasal verb, so unless someone tells me otherwise. It must be an idiom. It is certainly a noun, describing someone.