썩소, 썩쏘 Sseog So, Sseog Sso

'썩소 Sseog So', '썩쏘 Sseog Sso' is an abbreviation for a rotten smile. A sinister smile exudes evil, usually with only one corner of the mouth raised. It makes the viewer feel either awe or annoyance.

'썩소 Sseog So', '썩쏘 Sseog Sso' is 

A very slight smile when annoyed
or 

A very slight smile that exudes evil

썩소, 썩쏘 Sseog So, Sseog Sso

When using '썩소 Sseog So', '썩쏘 Sseog Sso'  add '날리다 Nal Ri Da' and use it as '썩소를 날리다' '썩쏘를 날리다'

source : https://namu.wiki/w/%EC%8D%A9%EC%86%8C