At the beginning of the clip, you can see a snow cloud of paper plates alighting on stage. An old tradition that continues to this day --fans requesting favorite Kinks songs by writing them on paper plates and tossing them on stage. (I remember two determined fans in Cleveland with a home-made banner they hung over the balcony requesting Waterloo Sunset and the utmost joy that emanated from that portion of the balcony when the request was granted at the encore.)
Flash is the attraction and allure of complete self-gratification and that tawdry glow that comes with being flush with other people's money. Flash is a Wall Street executive who made a lot of money on other people's misery and feels no regrets. He's a ponzi schemer and a hedge fund millionaire. As the song says:
There's no way that you can win,
You must obey his every whim
Or else he's going to do you in.
Here Comes Flash.
The rest of the sing along words can be found here.