That's bone, and the lettering is something called Silian Rail.
Some awful brat hurls frenetic and confused monologues of abuse and disturbed opinion at all and sundry on Youtube comments.
They continue to do this, replying to any person who argues back, with mounting vitriol and obvious veins popping near temples. They then mistakenly reply to their own comment in CAPS LOCK, pointing out what they think is wrong with the entire situation, and boasting of their pride at humiliating everyone.
They then go very quiet, and disappear from the page.