"... a word to use when in India, especially in Delhi. If you are a tourist you will be quickly singled out to either sell stuff to or be a target for con men.

Saying 'Cello' with an emphasis on the 'Che' at the start is local slang for "I don't want that." It's quite a forceful word to use however, so don't go using it on hotel staff but to the folks in the marketplaces and streets it suggests that you know your way around India a bit and they will tend to leave you alone."
Rob (Eastbourne, England)