Both expressions depend upon the context, but usually when you "have your fangs in" someone, you are criticizing them, making rude (or "poisonous") remarks about them, etc. It can also mean that you are treating the person as a sexual object and your own personal property ("None of the other women in the office were allowed to even say 'hello' to Brad once Patricia got her fangs in him; she was fiercely jealous.")
"Right off the top" can mean off the top of your head, but it can also mean "at the beginning" or "first." For example, "I want my percentage of the box office receipts right off the top, before you deduct any expenses."
Student or Learner