Ewe-ess-ens

take-off on 'usns'

Y'all are both right. It was derived from the first person dative/accusative pronoun but used in the nominative. At the same time it was intended to refer to citizens of the USA. In its most proper usage it wasn't intended to be used by anyone other than USns, but once it escaped the tips of my fingers it became public domain and, like children, no longer under the creator's control.