Surcharge

[Jessica]

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 females 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.

[Luis Fok]

a charge in addition to the usual amount paid for something, or the amount already paid:

[Dianne]

An additional charge or payment.