A key indicator of a successful (romantic) relationship is the willingness of each partner to use the other one's made-up words.Now the words don't actually have to be originally made up by the person; they could be historical family words that s/he just brought into the relationship. Traditionally, most families have words made up for bodily parts and functions.
In our case, a recent example is a word I made up to replace "dogs." I like addressing our two dogs as a unit, and I just felt like "dogs" didn't have enough syllables. So I started calling them "doggages," as in "Come on doggages, we're going for a walk." Julie took to the term, and so now they are The Doggages. It is an important part of the theory that words have to come from both partners... one-sided word generation suggests imbalance.
I am interested in more data points about the theory. I invite you to post to the comments.