Brownie Mix 

The act of sticking your thumb up your butthole then subsequently inserting it in your partner's butthole. Both parties then lick the content of their own thumbs similar to when licking the brownie batter off a whisk.

My girlfriend and I had some brownie mix after our Chipotle date.
My partner and I used brownie mix to spice up our relationship.

Brownie Mix by Browniemixlover69 August 8, 2021

brownie mix 

A person who is black on the outside and white on the inside or vice versa.

Oh you mean Joe, yeah he's a real brownie mix.

brownie mix by Goober February 20, 2015

Brownie Mixer 

The sexual act of inserting a mans fist into a girl's anus, then rotating his hand and extending his fingers (like a Kitchen Aid)

I gave my girl the ole brownie mixer, and she hasn'e been able to walk for a week.

Brownie Mixer by Tom Cledius November 11, 2011