My friend is divorced and I don't want a diamond ring. I bought it. What are the taboos of Feng Shui? How to avoid it?

First of all, this ring is only meaningful to their marriage, not to you. Remember to wash it in running water for a period of time (usually half an hour to an hour) after buying it, so that all kinds of bad luck of the former owner can be resolved. With a new owner, you will have no problem using the ring.