Why malaysian chinese do not respect other like talking in mandarin when other races are in the group/meeting?

Depends on the dialect that the Chinese community in the group is using. During official functions, usually Mandarin is used, but when conversing, it is up to the individuals whether to use Mandarin or Cantonese or Hokkien. It is really not a matter of not respecting the use of Mandarin but rather, we try to blend in the dialect that the other person is more comfortable with. Remember, not all Chinese know Mandarin or Cantonese or Hokkien.