Maybe just “D’eau” (smacks forehead)!
Seriously, as an Edinburgher, this is one of my earliest etymological memories; my primary head teacher used to give us some ‘local knowledge’. Like the area called Liberton was where the lepers were tolerated, a ‘tassie’ was a cup, and other French words that appeared as a result of the odd alliance that existed between Scotland and France at the time of the Jacobites, for example.
‘Gardez-vous’ (look out) was bastardised to gardyloo and the rest is up for debate, I guess!
Sorry I didn’t have more scientific data but there you go.