Domestic cat
Felis catus
Tasting sugar takes a receptor built from two proteins, made by the genes Tas1r2 and Tas1r3. In cats, Tas1r2 is a pseudogene: the code is still in their DNA, but it is switched off and never makes its protein. Without that half, the sweet receptor never forms.
Tigers and cheetahs carry the same broken gene, so the loss most likely happened in an early ancestor of the cat family. That suits animals that eat almost nothing but meat, which contains very little sugar. Dogs kept a working sweet receptor, which is one reason they beg for cake and cats walk past it.
Drop a sugar cube on a cat's tongue and it has no working receptor to register the sweetness.
