Thank You Come Again is a slur used to describe Indians in a derogatory way. A phrase made popular by stereotypical Indian convenience store owner Apu on The Simpsons.
The word Thank You Come Again 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 Thank You Come Again, it is best to err on the side of caution and avoid using it in any situation.