So much so that when this Hollywood odd couple sits down together in an interview for "Men in Black 3," the affable Smith plays it like couples counseling, launching into whiny-wife mode about Jones, his sometimes curmudgeonly cast mate.
"He doesn't compliment me when I get dressed," Smith whimpers on a sofa alongside Jones. "He'll just look at my clothes, and he doesn't say anything, and when we go out, he's always on his cell phone. And I just want him to think about me and my feelings."
What does his partner think about Smith's grievances?
"That's bull----," says the plainspoken Jones.
With a huge laugh, the two set aside the marriage session and get down to analyzing what has made their "Men in Black" action comedies a billion-dollar box-office franchise since the first movie debuted in 1997.
Jones had done big action flicks earlier in the '90s and won a supporting-actor Academy Award for "The Fugitive," but he wasn't an obvious audience draw for a special-effects summer blockbuster. Smith still was a comparative newcomer, breaking out on the big-screen only a year earlier with 1996's "Independence Day."
So at the start, the potential for "Men in Black" rested mainly on the clever idea of straight-laced government agents keeping in check the vast, secret comings and goings of some pretty far-out aliens on Earth.
Once fans saw the duo together, though, the franchise became those two guys - Jones' seasoned, surly Agent K and Smith's eager, convivial Agent J.
With 2002's "Men in Black II," even the actors concede they didn't get what they wanted - "the second one actually lacked originality," says Jones - yet despite poor reviews, the sequel was a solid hit.
Why? Again, it was those two guys, their opposites routine carrying things along even if the sequel's action wasn't as enticing as the first film.
"It's the opposition, man. It is like a married couple," says Josh Brolin, who co-stars in "Men in Black 3" as a young version of Agent K after Smith's Agent J leaps back to 1969 to save his partner from a time-traveling alien. "You look at them and you go, really, they're married? Then you just see they complement each other in the best of ways."
The rapport was there from the outset when they started working on the first film, and it came back in an instant when "Men in Black 3" began shooting, Jones said.
Smith, 43, already had a successful music career and a TV hit with "The Fresh Prince of Bel-Air" and had made an early mark on the big-screen in "Six Degrees of Separation" and "Bad Boys." So he came confidently into "Men in Black" but jokes that he had a fallback position just in case.
"For me, it felt safe, because if it didn't work, people were going to say, 'Tommy Lee Jones' movie didn't work,'" Smith wisecracks.
Jones, 65, was known for serious roles in such films as "Coal Miner's Daughter," ''JFK" and "Natural Born Killers." A newbie to comedy when he made "Men in Black," Jones says each sequel has been a cheery reunion, mainly because of Smith.
"Will is more generous than anyone, and he spreads joy," Jones says. "He walks into a studio, walks onto a set, and ... he makes certain that everybody's happy. He can't help himself."
"You gotta have fun," Smith says.
Barry Sonnenfeld, who directs the "Men in Black" movies, recalls that Jones was shooting on his own for two weeks on the first one while Smith was finishing "Independence Day."
That established a good foundation for the day their very different personalities - the reserved Jones testing his comedy chops, the jovial Smith teaming with an Oscar heavyweight - finally came together on set.
"Will came on to the movie that was sort of Tommy's set already, and I thought that was very helpful in retrospect. Because although Will would always be deferential and charming, Will is an 8-month-old Great Dane puppy, and he's got way too much energy, way too much joy, too much karmic perfection. And I think that might have affected Tommy," Sonnenfeld says.
"But Tommy and Will, from the very beginning, from the entire first movie, loved each other. Will genuinely feels Tommy's one of the funniest people he's ever met, because Tommy is George Burns and Will is Gracie Allen. You need both."
With Jones' K as straight man, Smith's J as comic foil, the "Men in Black" series has delivered one of Hollywood's most-enduring pairs of mismatched buddies.
"Partnerships are good engines for narrative," Jones says. "If you think of Don Quixote and Sancho Panza, the Cisco Kid and Pancho, the Lone Ranger and Tonto. On and on."
"It's the opposing energies for me," Smith adds. "Those opposite energies are so extremely spelled out. It's like the last two guys that you imagine are going to be partners, and there's no cross-over of each other's lanes."
The interview - or couples-counseling session - ending, Smith rises from the sofa, while Jones slips in a closing dig.
"Help me up," Jones barks.