Maybe this isn't precisely the word I want, but let me explain. My girlfriend watches many Thai soap operas on TV and whenever something bad happens to a character she doesn't like she's quick to blurt out to the TV "sohm-nahm-nah" or say the English, "serves you right." This happens often enough that I would like to in some way make her more aware of how others might see this.

Maybe this isn't precisely the word I want, but let me explain. My girlfriend watches many Thai soap operas on TV and whenever something bad happens to a character she doesn't like she's quick to blurt out to the TV "sohm-nahm-nah" or say the English, "serves you right." This happens often enough that I would like to in some way make her more aware of how others might see this.

not sure if I got you right, but som nam nah translates into Geman rather as "selber schuld". Still not sure what you wanted to point out.....

[still not sure what you wanted to point out.....

What I wanted to know was if there was a common Thai word or expression for someone who takes pleasure in the misfortune of others, or the word or expression that comes closest to expressing this sentiment.

The entry in Wikipedia gives the equivalent for schadenfreude in several languages (if it exists). Funnily enough, it gives the Thai version as SOM NAM NA สมน้ำหน้า, as you already mentioned. Maybe there's a closer expression...?

http://en.wikipedia.org/wiki/Schadenfreude

just asked my secretary, she came up with yok yoei and sum toerm - sory no Thai typing on my comp....