Written for a prompt from Tumblr user needsmoreresearch.
"He is so serious," Joly said, making a face, as if he were diagnosing Courfeyrac's new friend with a life-threatening ailment.
"Well, yes," Courfeyrac admitted. "There is no denying that. But he's not a bad sort. I do have some serious friends, you know!"
"Like who?" Joly demanded.
"Enjolras," Bossuet put in. "Combeferre. Feuilly. Jehan, when he's in one of his melancholic fits. Grantaire, in his own strange way—"
"Enough! You know what I mean. This Marius Pontmercy seems as though he never laughs."
Bossuet raised his eyebrows. "When was the last time you heard Enjolras laugh?"
"Enjolras rarely laughs out loud," Joly conceded, "but it's often obvious that he is finding something quietly amusing inside his own head. Like when he tries to make a pun, poor fellow. Whereas the inside of this Marius's head must be positively funereal."
He looked over at Marius, who was looking very uneasy, sitting next to Feuilly at a table on the far side of the Corinthe. Joly wasn't sure if it was Feuilly who was so discomfiting the boy, or if it was instead the presence of Combeferre, standing over the table next to Marius's, and laying down the law on some esoteric subject with his usual terrifying eloquence.
"We should rescue him," Joly declared. "We should teach him how to laugh."
"That is a fine idea," said Courfeyrac. "I have tried, but perhaps with the two of you by my side, I shall finally succeed."
"Surely we three, with our combined talents, can put a smile on young M. Pontmercy's face," agreed Bossuet. "It will be a challenge, but I feel we are up to the task."
Thus resolved, the three sailed forth from their table to descend upon Marius.
Ten minutes later, Marius had fled the Corinthe, mumbling something about a prior engagement. Joly gave him up for a lost cause. "I am agog, I am aghast," he said, "This Marius is an agelast."
Combeferre heard the last word and did not know what it meant, which gave Joly the pleasure of explaining it to him, and this, he felt, made up for Marius's flight—until Matelote, passing by, snorted, "You made that up, M. Joly. It's not a real word."
"I did not," Joly protested. "The Greek root, agelastos—"
"I believe you," Bossuet said, loyally. Joly, slightly drunk by this point, brightened at this, and felt that whole armies of agelastic Pontmercys could not sink his mood.