I've noticed that some of the default Visio shapes "flip" when glued to always face outward. How do I replicate this behavior in my own shapes?
Do you mean shapes like the Callouts? It's because they are 1-dimensional shapes.
No, it does this with 2d shapes. For example, gluing a triangle to a rectangle from the "Basic Shapes" stencil (after changing the connection point direction to inward/outward) results in the triangle flipping around to point away from the glued location.
Well, 1 = outward connector, Visio will attempt to align the connected shape in an outward manner.