These are the opening snippets of Bach's Brandenburg Concerto No. 2 - the opening of the 1st, 2nd and 3rd movements. I'll try to edit this by adding YouTube clips of performances of each movement. I just compiled such an excellent board when Pinterest failed me! I'll try again soon. ---UPDATE --- Pinterest have become bastards & won't let me redirect to great performances for fear I'm spamming. Pinterest is anti-educational!
The opening of the first movement of Beethoven's Symphony No. 1. This is a joke. I think it is Beethoven giving a major middle finger to conservatives and/or music critics as this great work begins exactly how it shouldn't - in the key of F Major, and then the Key of G Major. It is a symphony in C Major, so opening it intentionally in those keys, I feel, is part of a great musical joke. It then goes to C Major, as it should, but not after "ridiculing the rules." : )