[endeavour]

I don't think it's possible for something to be the 'most unique'.

[teach]

I used to be similarly pedantic with English. But a few years ago I converted to descriptivism[0], and I've been much happier ever since. :)

[0] http://english.blogoverflow.com/2012/10/prescriptivism-and-d...

[Confusion]

Not in a single metric. But you can formalize what is meant: there are many metrics in which something can be unique. Something is deemed the 'most unique' when it is unique in so many metrics that the utterer estimates no thing is likely to be unique in more metrics. Even mathematicians use sloppy language.