Rav Elchonon Wasserman practiced Shivisi HaShem L'Negdi Tamid ("I always envisioned G-d before me"). For that reason, he absolutely never laughed or smiled. Or perhaps it was in mourning over the destruction of the Bais Hamikdash: "Then (at its rebuilding) your mouths will be filled with laughter," but not until then. The only exceptions were when a mitzvah called for rejoicing, such as at a wedding; also, when he would quote the Chofetz Chaim, his face would relax into a slight smile. As part of this severe self-discipline, he would never slip a hand into his pockets. During the most biting cold of winter, his hands - red and frozen - would be gripping his coat buttons.