When you dont agree with something that someone says, or if someone says something in which you think is a "joke". This word is also applied when someone says something DAMN WRONG and you feel the need to emphasize the wrongness of it.
steve: deluc be hittin dat?
houck: you love him.
benbaby: uh.. skert.
teacher: today we will be reading pages 1- 130 in our books.
class including all tripple b's: SKERRRRT