Occurs when a man is engaging in sexual intercourse with more than one female partner simultaneously. During intercourse, anal penetration may take place. After the male genitalia has fully penetrated the female's anal cavity, the woman will place the penis back into her mouth This is commonly referred to as "Ass to Mouth" (ATM). A "surcharge" occurs if the woman placing the post-anal activity penis in her mouth is a partner other than the original recipient of anal sex. The name originates in the common practice of financial institutions charging an additional fee or "surcharge" for making a withdrawal from a third-party ATM.
Your mom, who you known quite the ATM machine, doesn't mind the surcharge with my friend, Nikki. What fun she is.