A tricky one. In the jock world, this refers to a protein shake with a banana blended in.
However, a notable non-jock, one K-Settle employs the term to refer to his fondess for fruital experimentation.
Jock: Man that was a tough workout, I'm gonna need a banana-buddy fairly sharpish to fuel my muscles.
K-Settle: Has anyone seen my banana-buddy? I need to muscle in up my fuel pipe.