Originally meant "warlike" or "aggressive." Now means "drunk" due to widespread misuse. But that's the idea behind urban words, so now it means drunk.
(Original) Archibald has been ruffling this fellow's feathers for nearly a fortnight now. I dare say he has been simply belligerent.
(Modern) Oh my gawd this muff cabbage pissed awl over Johnny B's carpet. What a belligerent bitch.