December 1988, in a school common room where my older brother was a sixth former, with a band without a name.
I just rang my bro and he can’t remember the first song either.
The set definitely featured some Poison, Def Leppard and er, Wild Thing.
VHS does exist of it somewhere, interrupted by someone announcing she was serving cake.
Added info: gear was my white Westone Spectrum ST bass into a borrowed Carlsbro bass combo of some sort.