allah, the exalted, says:

"and the (faithful) slaves of the most gracious (allah) are those who walk on the earth in humility and sedateness, and when the foolish address them (with bad words) they reply back with mild words of gentleness.'' (25:63)

703. `aishah (may allah be pleased with him) reported: i have never seen messenger of allah (pbuh) laughing so heartily that his uvula could be seen. he used to smile only.
[al-bukhari and muslim].

commentary: to laugh much is one of the sign of indifference to the remembrance of allah. besides, the habit of laughing aloud robs away the dignity and impressiveness of a man.