Son of a bitch is a pejorative epithet - a bad name to call someone. In some circles it is not considered very strong and may be used jocularly among friends. They synonyms in the WR dictionary entry might be enlightening.
Hmm..m..Seems I may be going out on a limb here so let me stress that my reply is my own thought and that I am at variance with the WF dictionary.
Thus: To Bitch/to be Bitchy about someone/something: Where one is making a fuss.
Son of a Bitch-Example of usage: If I hit my finger whilst useing a hammer and someone, say my mother, was within earshot I might say "O you son of a bitch" meaning the hammer was at fault and by inflection I indicate I might have used a far worse epithet.