If your classmate was describing you, you may want to check how you're coming across to others. Being ostentatious means you're faking or showing off — or both.
Pretending to be something you're not — whether it be rich with money, full of smarts on a subject, or so athletic you're bound to bring in millions of dollars and fans — might be somebody's way to impress others. But, if it's not the way it really is, it's just a made-up story.
Authors make up people and put them in situations to create a fictional story so that those characters can do, say, and act any way that gets the writer's point across. In everyday life, making stuff up can brand a person as dishonest, deceitful, or just plain silly.
From Jane Austen's Pride and Prejudice:
"Affectation of candour is common enough — one meets with it everywhere. But to be candid without ostentation or design — to take the good of everybody's character and make it still better, and say nothing of the bad — belongs to you alone."
In the words of Shakespeare, as spoken by Laertes in Hamlet:
Let this be so;
His means of death, his obscure burial, -
No trophy, sword, nor hatchment o'er his bones,
No noble rite nor formal ostentation, -
Cry to be heard, as 'twere from heaven to earth,
That I must call't in question.
And from Upton Sinclair's The Jungle:
Their life is a contest among themselves for supremacy in ostentation and recklessness, in the destroying of useful and necessary things, in the wasting of the labor and the lives of their fellow creatures, the toil and anguish of the nations, the sweat and tears and blood of the human race!