What should I do when I associate with groups of people who backbite, and I am unable to stop them? And is announcing one's abstention from backbiting on social media considered showing off?

Praise be to Allah, who guided the questioner to abandon backbiting and repent from it. It is obligatory for anyone who hears backbiting to rebuke its perpetrator and advise them; if unable, they should leave the assembly. The questioner's public declaration on social media that she has forsaken backbiting is a good deed, contributing to the eradication of evil, and is not considered hypocrisy.