The exact citation in English comes from a compilation of Napoleonic aphorisms published in London in 1848 by Count Caliste Auguste Godde de Liancourt, a globe-trotting aristocrat who spent his time founding humane societies and writing books about topics as diverse as shipwrecks, onomatopoeia, and Brazilian venereal diseases. The book is in French and English: the French version of the aphorism is:
Il faut rire des hommes, pour n'en pas pleurer.
For some reason the English version has man instead of men. Godde de Liancourt did not bother to cite the source for this quote. Some of the other aphorisms are easy to find because they were quoted verbatim, but this one was a tad more difficult to locate because the original quote is in fact different. Also, it seems more popular in the Napoléon-obsessed English-speaking world than in France.
The original quote can be found in the "memoirs" of Armand de Caulaincourt, close adviser and Grand Squire of the Emperor, the same guy who saw Napoléon committing suicide in Fontainebleau in April 1814 (see my recent answer here). These were not Caulaincourt final memoirs (hence "memoirs") but a shortened "oral history" version collected by Charlotte de Sor (Charlotte Eillaux) in 1826 and published in 1837.
Jean Hanoteau, who edited Caulaincourt's true memoirs in 1933, considered the 1837 version as a "tissue of absurdities, untruths and meanness of no historical value". However, while the 1933 version stops when the Emperor is sent to Elba, the 1837 version includes notes about the Cent Jours, the "Hundred Days", when Napoléon escaped from Elba and arrived in Paris on 19 Mai 1815.
The story told by Caulaincourt in de Sor's book takes place right after Napoléon's return in Paris, when he was trying to retake control of the country. He needed administrators loyal to him, but, because the "flight of the eagle" has been so fast, letters from notables willing to join Louis XVIII arrived at the same time as those of notables willing to join the Emperor. Caulaincourt to Charlotte de Sor:
In the interior of the cabinet some very pleasant things sometimes happened. The Emperor's progress had been so rapid that many letters to the King arrived at the same time as those sent to Napoleon, who took a malicious pleasure in pointing out the signatures of prefects or other authorities who had once been favoured by him. "That's what men are like!" he said with a pitying smile, "you have to laugh to keep from crying."
It expresses Napoléon's disillusion with the fickleness of men, in a "better to laugh than to cry" mode. How accurate the quote is we do not know, since this does not appear in Caulaincourt's final memoirs. It is true, however, that a number of men who had been honoured by Napoléon during the Empire had quickly sworn an oath of loyalty to Louis XVIII, and were somehow embarrassed now that the Emperor was back. Napoléon, despite his grandiose return to power, had a hard time finding support in a period of shifting loyalties.
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