As Barrs says, nothing to do with Notts C - it's hardly one of the bigger city football rivalries. Forest/Derby is the biggie in those parts.
He was despised at Forest due to his ridiculous, bullshit post-match interviews, his massive unjustified ego, his "direct" anti-football style of play, his lack of intelligence, persevering with tactics/players that don't work, bringing in physical "can do the dirty" types as opposed to play footballers with ability and nearly taking them down but for the saving grace of SOD coming in as coach.
Think that just about covers it.