To dream of defriending someone represents the choice to reject certain beliefs, people, or situations. Behavior, people, or places that were helpful are no longer interesting to you. Positively, it may be a sign that you are maturing or want to give up bad habits. Negatively, you may be in denial about your own faults.
Alternatively, defriending someone may reflect social disconnection or choosing to isolate yourself from certain influences.
Consider who it is you are defriending at what they may reflect in your own personality or a situation you are experiencing.