If you must stand because you cannot sit down for some reason, then it's fine to stand while eating; however, it is always preferable to eat while seated, relaxed, and enjoying food with all of your senses. Standing while eating is often associated with mindless, inattentive eating that may be unsatisfying but adds calories nevertheless.  And then some people stand while eating because standing burns more calories compared to sitting down, but that is an aberrant way of looking at calories and so it should be discouraged.