Acting tough: Bieber's UFC tweet to Tom Cruise sparks online craze to call out veteran actors

Since 25-year-old Justin Bieber's callout of 56-year-old veteran actor Tom Cruise to a UFC match, an internet craze has begun that sees social media users challenge Hollywood stars 31 years their senior to a fight.

On Sunday, the 'Baby' singer inexplicably called out Cruise, who starred in his first Mission Impossible film when the Canadian was just two years old, to a fight in the UFC octagon, tagging promotion head honcho Dana White in an attempt to make the fight happen.

Former UFC two-weight champ Conor McGregor then jumped on the hype, offering to host any potential match up, before going on to himself challenge actor Mark Wahlberg for his UFC stake. 

Most social media users were incredulous as to why Bieber would call out a man well past the prime fighting age, while also deriding the youngster - who doesn't exactly cut the toughest of figures - as having slim to no chance against Cruise.

Twitter users quickly picked up on the news, and quickly invented a craze of challenging actors exactly three decades and one year older than them to fight, beginning with 'The Killing Fields' star Sam Waterston.

A string of verified users got in on the act, enthusiastically calling out Hollywood's golden oldies, with older and even elderly screen stars being called out for a duel, regardless of their advanced years.

The result was a host of weird and wonderful pairings that eclipsed the initial peculiarity surrounding a Bieber versus Cruise match up - and no one was safe - with John Cleese and even Meryl Streep all getting the call-out treatment.

Others didn't seem so sure of their chances quite as much, and there were a range of lesser-fancied dust ups, from hardened Western star and all-round  macho man Clint Eastwood, Rocky and Rambo star Sylvester Stallone, to Sir Ian McKellen.

Surprisingly, US President Donald Trump made the cut due to his cameo appearance in Home Alone 2, in which he directs a young Kevin McCallister (Macaulay Culkin) to the lobby in one of his hotels.

So give it a try yourself. Who will you face off against under in the UFC octagon? Given his interest in the Bieber versus Cruise fight, maybe this could even be a new technique for Conor McGregor to match fights under his fledgling McGregor Sports and Entertainment banner.