I had a situation present itself that though it wasn't perfectly controlled could pass off for a double blind test. I was with friends and one went to get some coffee for both her and myself. The moment she put both coffees on the table she excused herself and took her phone out of the pocket to answer it.
I didn't know which was which (as I drink decaf because of genetic marker rs762551 that says I'm not metabolizing caffeine properly). So I thought how great this would be to test the difference between the two.
Both were Arabica and I was able to differentiate between the two with or without milk and sugar. The decaf version (I asked afterwards) was decaffeinated using the swiss process.
I cannot guarantee that both beans were the same even if they were both Arabica so it might just be that the beans were different.
My conclusion was that one of the two tasted sharper and more bitter. When she came back she told me which coffee was decaf and it was the one that didn't have the sharpness to it (or at least much less of it)
When I went home I googled to learn the taste of caffeine itself and the first hit I got was a site describing it as a sharp bitter taste.