Answer:
His name was given by his uncle Francis Adirubasamy. He taught Pi swimming and named Pi after his favorite swimming pool Piscine Molitor Patel. But people tease him calling him "pis sing" because Piscine just sounds like that.
When he moved to his new school, his class was introducing themselves and he had an idea. He went up to the board and wrote 'My name is Piscine Molitor Patel, known to all as Pi Patel.
He was alright with anything but "pis sing", even 'lemon pie'.