Like many on here I have close mates who are STH at the Temple of Doom, my sister is a red (typically, never goes the match, though!) and we can still get together for derby games.
For me it became less "friendly" with the onset of reserved seating. From the start of the 1995-96 season seats for Premier League games could no longer be sold on an unreserved basis and it made it much harder to be sitting next to the enemy at a derby. The issue over at the Pit where they have a high percentage agencies block-booking tickets going to daytrippers rather than regular, longstanding supporters does nobody any favours, either. As derbies have become more and more segregated there has been a more confrontational mentality at the grounds and some (note: some) people seem to be more interested in the opposition supporters than just backing their team.
Also, a lot of us Evertonians resent the treatment we have received at the hands of the local media over the years. It appeared that any off-field incident involving Everton supporters was subject to "special excusive investigation" whereas our neighbours farted floral fragrances. IMO, like.