If you really want to hurt someone’s self esteem, according to Self-Discrepancy Theory; first and foremost you will need to find out how a person views themselves... and secondly find out how they want to be seen by others. People direct their efforts in making a match between these two (hence the creation of self esteem). If you can create a mis-match between how they see themselves and how they want to be seen... you can impact their self-esteem in a negative way.
The way to create a mis-match can be achieved through the manipulation of the self-********** [one of three self motives (self **********, self verification, self enhancement)]. Sedikides (1993) suggested that the self-********** was the only self-evaluative motive that may cause a person's self-esteem to be damaged.
So... find out what accurate and valid information one seeks about themselves and contradict this information to create a mis-match. It might be more difficult the older the person is, as they could possibly have fewer reasons to seek accurate and valid information as they have created their own self identity.