To be secretly amused, whether in derision or just to avoid offense through open laughter, is to laugh in one’s sleeve.
The saying dates from the first half of the sixteenth century when, as one would suppose, the sleeves of a gentleman’s costume were distinctly oversize, large enough to conceal one’s whole head, let alone the mouth.
The French, at the same period and earlier, laughed in their capes, which were large and flowing; and the Spaniard could conceal his amusement by laughing in his beard.
