Roo is a slur used to describe Australians in a derogatory way. Commonly used due to their extensive supply of the specific animal "kangaroo", used as an offensive term to describe them and the way they walk. Often bouncing around and moving, like kangaroos.
The word Roo is a racial slur that has been used historically to degrade and dehumanize australians. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to australians. If you are unsure about whether or not it is appropriate to use the word Roo, it is best to err on the side of caution and avoid using it in any situation.