Ostentatious means showing off wealth or knowledge to be noticed. An ostentatious display, ostentatious generosity, less than ostentatious.
The point is the audience: ostentatious generosity is giving arranged to be seen, which is why the word can condemn a good act. It is always a criticism, and nobody has ever described their own behaviour this way.
1adjectiveostentatiousShowing off wealth or knowledge to be noticed.
“They live in an ostentatious mansion with gold taps and marble statues.”
ostentatious is a quality.
Latin ostentare means to display, a frequentative of ostendere, to show — ob plus tendere, to stretch.
Originated 1590; from ostentātus + -ious.
Etymology from Wiktionary, CC BY-SA