From Better Call Saul, season 6, Ep 7, Jimmy and Kim have unfolded their multi-step plan that is dedicated to undermine Howard in front of his colleagues, clients alike.

Throughout this TV series, Howard has been a good-mannered man, well educated and soft-spoken. Perhaps Howard had demoted Kim once during the city council embezzlement case, but the decision was made out of merit rather than personal grudge. Perhaps Howard has been a good friend with Chuck or Howard has a rich dad.

What provoked Jimmy and Kim to spend so much effort and time in order to undermine Howard in such a way which unintentionally ends his life?

If it is part of character-building, I do not understand. We have seen Jimmy has been pulling pranks in his younger days and Kim is caught shop-lifting once, but what warrants such an animosity towards Howard?