Do something more socially engaging than eating food and watching movies together.  A hot tub provides a more intimate and interactive way to socialize.  Have more meaningful conversations in a relaxed environment rather than sitting on chairs at a table or on the couch in front of a TV.  

Catch up with old friends, make new friends, stay in touch with your relatives.

Have your grown-up siblings over sometimes and go back to being kids again.

Jump in the tub after the BBQ instead of going back inside the house after dark.

Hot tubs are great places to socialize.  Let the hot tub be the host.