Speakers of English say “chop-chop” when they want someone to hurry up. The term is often directed at children and inferiors, and may be accompanied with a clap of the hands to underscore the urgency of the situation, and a desire to see the command obeyed promptly. While this term is closely associated with British English, it can be heard in other English-speaking nations as well.
The origins of this term are rather convoluted, and in order to get to the bottom of it, we are going to have to take to the high seas. Sailors have been using the slang term “chop” in a variety of senses since at least the 1600s, and when sailors started entering the South China Sea in large numbers, they were exposed to the Chinese term “k'wai-k'wai,” which means “hurry up,” or “get it done quickly.” Over time, sailors picked up the reduplication in the Chinese phrase, but started using their English slang term, and “chop-chop” was born around the 19th century.
When a word or sound is repeated to make a new word or for additional emphasis, it is known in linguistics as “reduplication.” Reduplication is a common feature in many languages, and it is especially common in slang terms. A related slang term from Hawaii, “wiki-wiki,” also means “hurry up,” and several other languages have similar examples of reduplication in slang terms which are meant to tell people to get a move on. Perhaps the reduplication is meant to express impatience or restlessness.
At any rate, “chop-chop” also entered pidgin Cantonese, a version of Cantonese spoken in ports around China which bridged the communication gap between Chinese and English-speaking sailors. English colonists and settlers also used pidgin versions of Chinese with their servants and staff, and chop-chop entered the landlubber's lexicon as a result.
Some people think that the term “chop-chop” is patronizing and offensive, because it was historically used as an expression of disdain towards servants and household staff by colonists. It could also be viewed as a corruption of a legitimate Chinese phrase, rather than a slang term in its own right, and some people prefer not to use it for this reason. Ultimately, the decision to say “chop-chop” or not is up to you, although you may want to ask yourself how you would feel if someone was shouting “chop-chop” and clapping his or her hands at you to get you to hurry.