Green’s Dictionary of Slang

shampoo n.

champagne.

1959		A. Sinclair Breaking of Bumbo (1961) 24: What will you have? Shampoo or gin?
1976		P. Theroux Family Arsenal 257: ‘Shampoo,’ said Lorna, handing Hood a glass of champagne.
1985		R.G. Barrett You Wouldn’t Be Dead for Quids (1989) 54: A couple of bottles of French shampoo, son, Dom Perignon 72.
1999		K. Sampson Powder 399: Guy’ll be up in a minute. Let me fire the shampoo in.
2000		J.J. Connolly Layer Cake 68: You want some shampoo, mate? He’s got a bottle of Champagne by the neck in his hand.