usually written in all caps, hollervision is the moment of surprise that happens when two friends run into each other at an unexpected moment and make eye-contact simulatneously in a way that both parties can see each other's surprise and thus, aknowledge each other's presence.
In a way it is like giving someone a "holler" just through eye-contact.
Woah Stevie! Never thought I'd bump into you at this mall! That was some intense hollervision we had going on eh?