A show-off is a person who attracts attention by frequently demonstrating their talents. The tone of the word varies depending on the speaker's relationship with the subject, although it is most usually employed in a mildly mocking manner.
Describing somebody as a show-off carries an implicit endorsement of their capability: someone can only "show off" if they actually have something to show. An individual who seeks attention that they are not perceived to deserve is described much more dismissively as an attention-seeker, loudmouth or hypocrite (besides a host of less flattering names).
