The late-night host broke more than usual as the two flung facelift and Nazi memorabilia jokes at each other on the show.
The game mimicked the rules of the traditional Newlywed Game, with Fallon asking the longtime friends random questions about each other in the hopes they'd come up with the same answer.
Fallon's first question: "If Martin won the lottery, what would he buy?"
Steve's answer was "Friends!" Fallon laughed hard, but not as hard as he did when Martin revealed his answer: "Another facelift, but this time, with a real doctor."
Fallon's next question: "If Steve could be any liquid, what liquid would he be?"
Martin said, "I wrote skim milk because he looks like a glass of skim milk."
Steve took the boring route, answering, "Why would I want to be a liquid?"
"That's a very Steve Martin answer," Fallon said before asking his final question: "Complete this sentence: Steve has the world's greatest blank."
Martin's answer: "The greatest collection of Nazi memorabilia."
Fallon burst out laughing. "What is wrong with you, man?! What is wrong with you? That's absolutely not true," he said.
Steve wrote -- get this -- the exact same thing.
"Oh, my god!" Martin exclaimed. "We are best friends! We are!"