That never happened.
But I do still enjoy the movies and happily watch them again whenever they are rerun around Christmas time. I suppose the whole concept of time travel appeals to my nerdy nature, which is great. But that same nerdy nature has ruined Back to the Future 2 for me, because of a fatal plot hole. The whole second-half of the movie makes no sense when this plot hole is considered.
It goes like this...
With me so far....? Good.
Does anything about those series of events strike you as being wrong?
OK.....if you haven't spotted it already here comes the plot hole...
Why does the past/future only change to the 'rich Biff' reality when Marty and the others travel back to 1985? It should have changed before they travelled back. Think about it. When the old Biff gives his younger self the sports almanac, he then travels back to 2015 and returns the DeLorean in what is still a 'poor Biff' reality. But that's wrong! The moment that he arrived in 2015, it should have automatically been a 'rich Biff' reality.
The implications of this small plot hole are massive.
The moment that the old Biff gives his younger self the sports almanac, all future scenarios would automatically become 'rich Biff' realities. That means that the 2015 future that the old Biff left would not exist anymore, meaning that it is highly unlikely that the future Marty and Doc were still trying to rescue Jennifer. In fact, we find out that in the 'rich Biff' 1985 reality, Doc has gone crazy and has been institutionalised. Based on this, it seems doubtful that he would build the time-machine and team up with Marty as had happened originally in the 'poor Biff' 1985 reality.
Of course, no time machine means no DeLorean in 2015 for the old Biff to steal. Which means that Biff can't give himself the almanac and become filthy rich thus creating the 'rich Biff' reality. This creates a paradox in which the 'rich Biff' reality actually prevents the future creation of the same 'rich Biff' reality.
The universe will explode in 5, 4, 3, 2......
......or it could just mean that time travel in a 1980's sports car isn't possible.
Good movie though! :)