Collocations for improper - adj.

be, seem
consider sth, regard sth as, think sth (esp. BrE)
places where it is considered improper for men and women to kiss in public
They thought it quite improper for a woman to smoke.

highly, most (esp. BrE)
quite (esp. BrE)

Improper is used with these nouns:
conduct, exercise, fraction, influence, trading, use