I think I must be one of those people who can detect the slightest difference in things. And I mean slight. I know when something is off by even the tiniest bit while others can detect no difference at all. When I worked in a lab setting, I could tell by the way things looked, smelled, or acted if there was something wrong with the sample, the reagents, the process, possible contamination or if something like a gene splicing protocol didn't work. And I can also detect some color variations so slight that other people say they can't detect. One time I was in one room and was listening to a large centrifuge running in another--this thing was the size of a washing machine. It started making an oscillating noise so slight and so fast that no one else could hear it, it was very high pitched, but I insisted something was wrong with it. I went to get the CEO of the company and tell him when BOOM!, the centrifuge tube went completely through the side of the machine and was embedded in the sheet metal exterior wall, like a missile. The machine had a hole the size of a laundry basket in it, it was completely ruined.
I assume I have more sensitive senses and I know when something isn't quite up to snuff. So to speak. I couldn't detect any difference in the old coffee vs. the brick of coffee that I had just finished using.
And I agree about the milk smelling bad because it's what has dried on the threads of the milk jug. Story telling on myself--once I was super thirsty and hungry and had been working out in the heat. Came inside and thought a few nice glugs of cold milk would be delicious. I opened the jug (1/2 gal.) and without hesitation turned it up and started drinking, I was very thirsty and just started slugging it down. After the fourth slug I realized it was pretty thick. And it was putrid. Clabbered isn't the word for it. It was beyond clabber. It's a good thing I have a strong constitution. I thought for a second I might throw up, but it stayed down just fine, if a little squicky feeling in my stomach.
I really enjoy hearing about what other people have actually tried and how far past it's 'best by' date it was.