One of the most famous episodes in Ramayana (especially on television) is that of Angada or Angad sitting on a seat made of his tail in palace of Ravana in Lanka. Please note that this episode is not part of Valmiki Ramayana but is found in the Ramacharitamanasa of Tulsidas. Ramacharitamanasa only mentions about Angada in the assembly but it does not state that Angada sitting on his tail.
The episode takes place in the Lanka Khanda of Ramacharitamanasa.
After reaching the island of Lanka, Rama and the army of Vanaras decided to send an envoy to Ravana for a peaceful settlement. When Angada reached he was challenged by Prahasta, a son of Ravana. Angad easily overpowered and killed him by seizing his foot, swinging him round, dashed him to the ground.
The demons that saw this dreadful act thought Hanuman had returned back to burn down Lanka again.
Soon Angada reached the court of Ravana and his enormous form send shivers down the demons assembled in the court.
As per some regional versions and folklore, a haughty Ravana denied Angada a seat in the assembly. Angada elongated his tail and converted it into a seat on par with the throne of Ravana and sat on it. But this incident is not mentioned in the Ramacharitamanas and Valmiki Ramayana.
But Angada did show his valor and courage in the court of Ravana as per Ramacharitamanasa of Tulsidas. Ravana insulted Rama and monkey army. An angry Angad gave a scream that was so loud that it caused demons to tumble down from their seats in the assembly. The crowns of Ravana too came rolling down and Angada hit some of them as far as the camp where Rama and the monkey army was stationed. Angada then challenged Ravana and other demons to stir his foot which was placed in the middle of the assembly. But Ravana, his son Meghnad and other powerful demons failed to move the foot of Ravana.