Did Al-Abbas, the uncle of the Prophet, peace and blessings be upon him, mock him?

Ridicule of the Prophet, peace and blessings be upon him, is, by consensus, one of the nullifiers of Islam. Al-Abbas ibn Abd al-Muttalib, may Allah be pleased with him, is a venerable Companion, so it is inconceivable that such an act would emanate from him. What you mentioned is among the falsehoods of the people of innovation who are unjust towards Al-Abbas, may Allah be pleased with him. One should be wary of being drawn into everything that is published on modern social media, as it contains both valuable and worthless content.