It's fighting talk.
All shiksas are shit.
I fucked that shiksa and gave her the clap.
Traditionally this is a derogatory term, though in modern times it has also been used more light-heartedly. For example, Seinfeld once did an episode about Elaine's "shiksa appeal".
The ideal shiksa is a blonde WASP who look like the opposite of a stereotypical Jew, but in reality, many shiksas are brunettes who might pass for Jewish themselves.