In America, we'd say something is "crazy" if it's unbelievable or surprising (or indeed crazy). In London, the equivalent word is "mad". As in, "He's gone mad!" or "That's absolutely mad, man!"
Just heard this song, yo! It's a MAD TING! An absolute mad ting.
An absolutely foolproof way to keep minors from viewing content deemed "too mature" for them to watch.
Billy: "So I was trying to watch some videos for an M rated game, and I ran into an age gate, so I put in my real birthday. SOMEHOW it managed to figure out that I am 12. CURSE YOU AGE GATE!!!"
Bill: "Fucking age gate! *quick scroll* THERE! I was born on January 1, 1904. Fuck you age gate."