Unable to be damaged or broken unless certain circumstances arise. He is invulnerable to insults because he his deaf. See invincible.

Antonyms: vulnerable mortal breakable soft flimsy breakable
Synonyms In-penetrable, fortified, unbreakable. Tough.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.

Theres a difference between somebody thinking they're invulnerable, and knowing that they're not invulnerable, and that they can get sick, get hurt, or get dead, and still keep going/enduring anyway.