"Don't bark if you can't bite" is a proverb which actually means in two different ways as follows.
1. If one cannot do a work, he must not command any other person to do the same work that he can't.
2. One must not make a promise if he can't keep his promise up.
i.e. if a person does not know anything, he should not behave as if he knows everything which otherwise can lead to a worser situation.
This proverb should not be taken in its literal meaning.
(Usage of the word "bark" - "Dogs bark on seeing strange people")
1. Raju could not do the work that he promised to do. So, his manager used the hot sentence "don't bark if you can't bite".
2. Kishore's friend could not keep his promise that he made to him and so Kishore said to him "don't bark if you can't bite".