Britney Blows up .

Britney is turning to be as bad as she looks . Recently, this trailer park trash was heard shouting expletives at her mother .

An eyewitness on the set of Zoey 101, the TV show starring Britney's younger sister, Jamie Lynn, 14, tells Star People: "Britney was screaming at her mom. She was furious, swearing and cursing. Her mom burst into tears at one point, but Britney didn't seem to care or notice."

The June 30 bust-up erupted just as Britney, 23, and Lynn, 50, were leaving the set for the day.

"Britney began yelling at her, saying that her father [Jamie, 52] was sometimes not there for her and that Kevin will be the best father for her baby," the witness says.

"Britney's mom got really upset and began to cry. She told Brit that her father does love her and that he did the best he could for the children.

"But Britney wouldn't listen. She got into her car and sped off, screaming 'Fuck you, momma!' Everyone was really shocked and stunned."

Such a cow . Of course , we understand that being pregnant brings out a very emotional side of yourself , but only mums-to-be carrying Kevin Federline's baby can resort to such level of crude behaviour.