Ostentatious IS a verb. To be ostentatious means you are showy.

It was an ostentatious presentation of food.

The room was decorated in an ostentatious manner.

His clothing was ostentatious.

As "ostentatious" means "unnecessarily showy" or "extravagant", an example of something ostentatious would in general terms be anything where unnecessary additions or "extras" are involved. Particular examples would be "ostentatious dress", "ostentatious manners", "ostentatious display of money", even "ostentatious use of examples".

Yes, I can. "At the party, she was both loquacious and ostentatious."

Example sentence - Her ostentatious remarks were going to haunt her for years to come.