There was a never-to-be-forgotten occasion when my younger daughter spread Very Good Home-Made Marmalade on a slice of toast using a knife that had previously been used to spread garlic butter on bread.
Garlic butter is very good.
Very good home made marmalade is very good.
The two combined are utterly dreadful. It's not just that the taste is bad, it that you realise that lovely slice of toast with marmalade has been utterly ruined and has to be thrown in the bin.