The Bodhisatta was once a king’s advisor. When the king died, his advisors had to choose a new king, and they planned to pick the young prince. But the Bodhisatta did not agree with this decision because the prince was extremely lazy. They decided to test the boy by having him watch a mock trial, and they intentionally made the wrong decision. When they asked the prince if they had judged it correctly, the boy curled his lip. This made the Bodhisatta think he had seen through their ruse and was in fact wise. The next day, they arranged another trial, and this time they did judge it correctly. Again they asked the prince what he thought, and when he made the same lip curl, the Bodhisatta knew he was in fact a blind fool. The Bodhisatta was made king instead.
In the Lifetime of the Buddha
The lazy prince was an earlier birth of Laludayi, an elder disciple of the Buddha who was quite stupid. One time after Sariputta and Moggallana, two of the Buddha’s top disciples, had discussed a question, the other disciples praised them. But this foolish disciple thought his knowledge was equal to theirs and curled his lip in scorn.
When the Buddha heard the other disciples discussing Laludayi’s disrespect, he told them this story so they knew that he had also shown his foolishness through lip curling in the past.