Unworthy offspring brag the most about their worthy descendants.
— Danish proverb

It's not bragging if you can back it up.
Muhammad Ali brags quote

If I seem to boast more than is becoming, my excuse is that I brag for humanity rather than for myself.
— Henry David Thoreau

If I cannot brag of knowing something, then I brag of not knowing it; at any rate, brag.
— Ralph Waldo Emerson

Those who boast of their descent, brag on what they owe to others.
— brags quotation by Marcus Annaeus Seneca Seneca The Elder