For me it's limited to a few. For the rest, either I can't taste them or I have never tasted them!
But the ones I can taste, by jaysus they scream at me!
- Diacetyl. Butterscotch, and quite nice in some beers. Getting it a lot in Ór lately.
- Chlorophenols. I seem to be uber sensitive to these and can taste them before most other people can.
- Wild yeast. Aka Belgian yeast or dishwater flavour. Again, very sensitive to this, moreso than most it seems.
- Mercaptan. Sewerage smell, not so much a flavour.
- Acetobacter. Bug that turns alcohol into vinegar, but I think most other people can taste this at the same level as I can.
- Acetaldehyde. "Green apple". Doesn't scream at me, but I can usually get it, especially if it's pointed out to me.
Can't say I've ever had any of the other common off flavours!
'water' is an off flavour I detect in certain American lagers.