It all left captain Steve Smith, who sat by his side for what will surely go down one of the most peculiar press conferences in test history, in stitches.
It was the first time Smith, whose unbeaten 141 was key to Australia's victory, had lost his composure in five days.
"Goodness. I can't talk," Smith laughed.
At Perth's Avenue Bar, West Australian players were celebrating their Sheffield Shield win over Tasmania when the England team strolled in.
"I remember it very clearly," Bancroft said. "It was very friendly, mingling the whole night. Obviously some of our players knew the English players," he said. "As the night progressed it was great to be able to meet some of those guys. I got into a very amicable conversation with Jonny and, yeah, he just greeted me with a headbutt.
"It wasn't the greeting of choice I was expecting. A handshake or a hug or something like that would have been something that I probably would have expected more than a headbutt, but there was certainly nothing malicious about his action.
"I don't know Jonny Bairstow but he says hello to people very differently to most others."
Bancroft said it was "random" but a "good hit, play on."
"He connected with my head, with a force that would make me sort of think, 'wow, that's a bit weird'," he said. "And that was it.
"Headbutts clash with heads. When he made the decision to do that, it meant our heads collided."
Asked if it was how he envisaged his first post-match press conference as a test player would go, he said: "Not really, no. But it's all good humour, isn't it. I'll look back on this one day and it'll be a dot in my life."
England Cricket Board chief Andrew Strauss played down the incident, describing it as "playfulness" that had been "blown out of proportion".
The ECB investigated the alcohol-fuelled incident that unfolded almost a month ago after Australian players were heard sledging Bairstow about it in the first test. Australian vice-captain David Warner could be heard saying "you shouldn't headbutt our mates" before umpire Marais Erasmus intervened. England team insiders claimed the keeper was a "rugby man" and part of their culture was an odd habit of bumping heads after someone buys them a drink.
Either way, former England great Ian Botham wondered why Australia were bringing it up now.
Former Australian test bowler Brendon Julian claimed the Australians blurted it out over the stump mics so the story would be leaked. "... they're on top... and are thinking 'well let's just do something else to just sort of niggle away'," he said.
