5 UFC Stars Tell Real Life Street Fight Stories, 'I Know I Can Kill Somebody'

Every UFC superstar has an origin story -- a fight experience that convinced them they could brawl for a living ... and 5 of the toughest guys in the sport told their stories to TMZ Sports.

Justin Gaethje, Kamaru Usman, Henry Cejudo, Kelvin Gastelum and Ottman Azaitar joined the TMZ Sports crew for a 30-minute, no-holds-barred convo about everything from upcoming fights to real-life fight stories and how UFC fighters REALLY feel about Conor McGregor.

Gaethje walked us through how he's been trying to draw out Conor into a fight -- but the Irishman seems to be ducking him. He also wants a fight with Khabib Nurmagomedov.

Kamaru explained why his beef with Colby Covington is 100% real ... and why he wants to "separate him from consciousness" when they fight at UFC 245 on December 14.

Henry told us why he believes he's the greatest combat sports athlete of all time ... better than Muhammad Ali, Bruce Lee and more!!!

Kelvin called out Israel Adesanya for a rematch ... and revealed for the first time that he was sick and way less than 100% when they fought the first time at UFC 236 in April.

Kelvin says he was diagnosed with a staph infection before the fight but battled through severe illness to get in the octagon ... and he still almost won!!!

Now, Gastelum says he REALLY wants a rematch to prove he's the middleweight king.

Ottman, who had one of the best KOs of the year, tells us what it was like fighting with a broken hand ... and scoffed at Evan when asked if he ever considered quitting during the fight. Dude's tough as nails.

And, Ali Abdelaziz, who manages all of the fighters -- along with Khabib -- told us why he thinks Conor is one of the worst human beings in pro sports.

Also, 2 of the guys make a real pitch to become the next 'Bachelor' ... and they're dead serious about it.