If you say that someone is overdressed, you are criticizing them for wearing clothes that are not appropriate for the occasion because they are too formal or too smart.
overdressed in British English
(ˌəʊvəˈdrɛst)
adjective
dressed too elaborately or finely
She was overdressed for the party.
Examples of 'overdressed' in a sentence
overdressed
Corbi had moved off with the overdressed Count and his friends and they soon disappeared from view beyond the trees.
Nabb, Magdalen, Vagheggi, Paolo PROSECUTOR (2001)
There was a woman standing a couple of yards from the front gate: large, pale, and overdressed.