"Marriage" is one eight letter word.
Saying "we're going to get civil unioned tomorrow" is just weird, as is writing "civil unioned" on the back of your car.
Telling the hotel clerk that you were "civil unioned" is kind of freaky, too.
Telling your friends that you're the best man at someone's "civil unioning" is both kind of awkward and might be misconstrued, too. You might leave them wondering if you're the bottom or the top, instead of just an adjunct for the two players.
And telling your aggressive secretary that you're a happily "civil unioned" man will just cause him to crack up.
And in the area of apparal, would the "union suit", you know, the long johns with the flap in the back, take on a whole new image in the eyes of the public?