He thinks everyone's supposed to be mad.
`Oh, you can’t help that,’ said the Cat: `we’re all mad here. I’m mad. You’re mad.’
self deprecating modest about or critical of oneself, especially humorously so
Answer:
means someone's sarcastic
Explanation:
"That person is caustic," means "That person is sarcastic/mean/harsh." If someone says something "caustically," it means that they are saying something in a sarcastic/hurtful way. Hope this helps. :-)