Would one be punished for performing voluntary acts out of embarrassment, not seeking reward or out of showing off?

The acceptance of deeds requires two conditions: sincerity of intention to Allah Almighty, and conformity with the Sunnah. Therefore, you will get nothing from your action except what you intended, which is to remove hardship; as the Prophet, peace and blessings be upon him, said: "And indeed, each person will have what he intended." You bear no sin, as there is no Sharia transgression, and you will receive no reward, as there was no intention of seeking recompense.