Stands for Bitch My Life, a commonly used expression to express any emotion, such as anger, depression, stress, or arousment.
Ginger: I have a english essay due tomorrow that I haven't started. BML.
Girl #2: Don't worry, I'll bitch it, I'll bitch it real good.
Ginger: Oh god, BML, that poodle is staring at me.
Girl #2: BML, I'm so aroused!