Curiously inconsistent in what is accepted. Betty Boop accepts neither first name nor last name and requires booth. Catwoman only accepts the 'fake' name and not Selina nor Kyle nor Selena Kyle. Lois Griffin accepts just 'Lois'. Lara Croft requires both names. Etc.
As far as the inconsistency goes, some names just belong together. Fred's catchphrase is "Wilma!" So I accepted just that.
Hayley Smith doesn't require a last name because in the show the last name rarely matters.
I consider Betty Boop as a whole.
Same as Lara Croft. Nobody ever calls them by only their first or last name.
Hope you understand my point of view.