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3.
Two black males who also happen to be butt buddies, or gay sex partners.
Bro, Kobe is definitely butt brothers with that ref.
by BHG42 May 01, 2012
 
1.
Gay buddy that meets you on occation to "fuck" and also happens to be your best friend. (man on man only)
Hey did you know that steve, joes best friend is a "Butt Brother" and they fuck on occation. (
by scott pitts February 16, 2005
 
2.
The connection two men gain after they share a common toilet seat. Similar to Blood brothers, but hopefully, no blood is involved.
After Jason took a dump in our shared bathroom at work we became "Butt Brothers."
by foureyedg November 16, 2009