14 years - as long as 1970-1984 was.
Anyway it's mostly because we've been too worked up in the past 3-4 years, when we should realise we are at least their equal, to just treat it as another game. When we were vastly inferior to them (let's be honest just about every year bar 1985-1988 since the 1970 title winning side) we really had two chances (in reality just the one, at Goodison) to give their all-singing all-dancing winning side a bloody nose. So we invariably went at it like a bull in a gate to give them a hard time. Once in a while it actually worked.
I don't have a problem with treating a better side this way - give it 100% and see where it takes you. It never was much use for our mid-table journeymen (in the past) to take this match as just another game. Now however we are, at the very least, their equal - and in the past two or three seasons better than them. So a new strategy is required where we have to cope with their desire to put one over us and find a way (as they used to) of playing our own game and establishing control. I can barely remember us going to The Pit and being the better side (maybe 2 or 3 times in the past 20 odd years). So it's time to take it as another game and give them what they deserve - a bloody good hiding.