Getting pregnant outside of marriage.
Nutella (it wasn't sold in the UK when I was a child so we only ever had it while on holiday in France...it was practically the highlight of the holiday and my mum used to bring the jars home to use as glasses)
Forgetting to set the VCR to record your favourite programme if you were going to be out. If you didn't record it, that was it - no catch-up!
Australian soaps (Neighbours, Home & Away) - everybody I knew watched them and each episode was earnestly discuussed at school the next day. Because the whole country watched the same episode on the same day, it was a unifying force, a national obsession, in a way that TV isn't now. Same with the The Thornbirds.