Why do people say Whatever Trevor?

In the U.K we watch a soap Opera/drama called Eastenders. An episode with Little Mo who was married to Trevor. He was a violent and abusive husband, the manipulationlead to her isolation from her family and an affair which she uncovered. One day she had enough and bashed him over the head with an Iron. The he saying "Whatever Trevor" highlights the extreme nature of his abuse. And the situation of being stuck in a cylcle of abuse.