When you have anal sex with girl, and then switch to vaginal sex when she is on her period.
From the Chicago Elevated Train lines, Fullerton is a stop where one can transfer from the BROWN line to the RED line.
My girl was on her rag, so I was fucking her in the ass. I really wanted some pussy, so I did a fullerton transfer.
A Chicago Transit Authority El station that connects the Red, Brown and Purple lines. In this case, it involves going from the Red to the Brown, or the Brown to the Red. If done right, it'll leave Purple bruising.
For additional style points you can give her the "Skokie Swift" (Yellow line) and hose her down in a golden shower.
"I rawdogged this chick's bloody snatch then I flipped her over and gave her the Fullerton Transfer."
A transfer from the Red Line to the Brown Line
A Fullerton Transfer occurs a guy is having sex with a girl and then pulls out of the girls vagina and puts it into her butt.