Madrasis is a slur used to describe Indians in a derogatory way. The biggest city in South India used to be called Madras(now Chennai).
The word Madrasis is a racial slur that has been used historically to degrade and dehumanize indians. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to indians. If you are unsure about whether or not it is appropriate to use the word Madrasis, it is best to err on the side of caution and avoid using it in any situation.