Kosh - Absolutely fight Kosh. You probably won’t win, but my god will the rest of us find it satisfying. In fact, fight as many Vorlons as you can.
Sinclair - Please. His eyebrows alone could take you. And don’t think of waiting until he’s (sadly eyebrowless) Minbari Jesus, okay, because you’ll piss off the entire Minbari race and that never ends well.
Vir - You could, but why would you want to? Give him a hug instead. Duration of hug depending on which season he’s from.
Byron - Please. For all of us.
Londo - I don’t think you can avoid it. Londo starts fights, and even if he’s obviously outmatched, he won’t give up. There will be blood and tears and no one wins this one.
Lyta - She’ll melt your brain. Just leave her alone.