34-year-old Gaethje, the #3 ranked UFC lightweight, joined Babcock on the "TMZ Sports" TV show (airs weekdays on FS1) ... where we talked about everything from who he wants next, to how he'd fare against the current champ, to how much longer he sees himself fighting, and Conor McGregor recently calling him "handicap" on Twitter.

On who Gaethje, who is coming off a dominating win over fellow contender Rafael Fiziev at UFC 286 in March, wants next:

"I think that's the obvious choice, Dustin. He's sitting at number 2 right now, I gave the new guys a chance and I proved that I am elite, and I need to fight elite fighters to fight for a belt. I think Dustin's the obvious choice. I think the loser of Dariush and Oliveira is also an option, but outside of those two, I do not see an option."

FYI, Justin and Dustin fought back in 2018 ... a classic fight that Poirier won by fourth-round TKO.

Of course, Islam, who was just in battle with 145 lb. king Alex Volkanovski (Makhachev won by the thinnest margin), is the lightweight champ. We asked Justin how a fight between the men would look.

"I think [Islam is] a hard fight for anybody. Just create damage. I'd have to fight the perfect fight," Gaethje told us, adding he recognizes he wouldn't be on the Dagestani fighter's level when it comes to "submission grappling," but Justin believes with his power, he can shut anyone's lights out.

"I think I can knock him out. I think I can knock anybody out with the power that I possess."

We asked Gaethje, who lost by submission to Khabib Nurmagomedov in 2020 at UFC 254, to compare The Eagle and Makhachev.

"I think they're very similar. I think the biggest difference is Islam has been finished. He's lost a fight. He's been finished. So that aura of invincibility is there, but it's not based on 100% facts like Khabib has, I think that's the biggest factor, the biggest difference."

We also talked to Gaethje about retirement.

"I have never thought about retirement. I haven't thought about my life after retirement. I'm still working for the goal that I've set for myself," Justin said, explaining he has faith that his family and friends would tell him when it's time to hang up the gloves. But, that's likely years away, according to JG, who believes he's just hitting his stride as a fighter.

"34, I think we are at our peak, mentally, physically. Between 34 and 36, so I can't see myself being done in the next two years. I'd say two to four years is def a timeline that makes sense. I'm not trying to fight when I'm 40, and after 36, I don't see myself getting better."

Lastly, Conor recently tweeted "Justin Gaethje is a handicap," before deleting the message shortly after. We asked JG for his reaction.

"One of my best approaches in life is to make everybody think you're stupid and then go into a conversation or situation where you can take advantage of everybody feeling like that. It plays perfectly into my hands. I love when people think I'm handicapped or dumb -- that's not a guy, I don't believe I'll ever fight him."

Gaethje vs. McGregor is a fight fans clamored over for years ... but Justin says the guy simply doesn't want to step foot in The Octagon with him.