That doesn't make any sense. If the milk looks old, I'm not sniffing or drinking it.

I'd consider calling the manager and complaining.

What if the milk is already in your fridge?

Who was in my fridge??

I'm not milk, but you can still sniff me if you want.

Milk

God dammit. I'm calling the manager!

Moooo

It does though, the reason it's relatable as a joke is that it's a somewhat common scenario. It's not that people sniff milk when it's bad, they do so to determine if it's bad, and that's usually done in a circumstance where you need milk and only realised that the milk you have and need now might actually be suspect and should be checked. It's also one of the few foods where such a test is fairly accurate and the risks of illness are pretty low which is likely why it's a fairly common thing that people do.