Full Idea
There is no complete ordering of people by niceness, and two people could be both fairly nice, nice to intermediate degrees, while there is no fact of the matter about who is the nicer.
Gist of Idea
People can't be placed in a precise order according to how 'nice' they are
Source
R Keefe / P Smith (Intro: Theories of Vagueness [1997], §4)
Book Reference
'Vagueness: a Reader', ed/tr. Keefe,R /Smith,P [MIT 1999], p.43
A Reaction
This is a difficulty if you are trying to decide vague predicates by awarding them degrees of truth. Attempts to place a precise value on 'nice' seem to miss the point, even more than utilitarian attempts to score happiness.