On Sunday morning (AEST), at Madison Square Garden in New York City, we saw an example of normalisation.

A decade ago, the idea of the Ultimate Fighting Championship planting its cage amid one of the world's most iconic sporting arenas would have seemed laughable.

But here it was, and top of the bill was an Irishman called Conor McGregor, a two-weight world champion you might describe as the Donald Trump of UFC: a man with a talent for exaggeration and demagoguery, an unabashed fixation with money, fame and physical might.

"I'd like to take this chance to apologise to absolutely nobody," he said after a brutal second-round knockout. "The double champ does what the f--- he wants."