Buddy of mine had a batch of C-41 go bad in the bottle, smelled like old gym socks and gave him weird color shifts. Ever had a developer go south on you like that?
Smell it before you use it, that's my rule now. I had a bottle of Rodinal that went funky on me once, turned into something that looked like swamp water and smelled like a dead fish left in the sun. The negatives came out all cloudy and muddy, like someone took a photo through a dirty window. Learned that lesson the hard way, now I check my chemicals like I'm sniffing milk before a cereal pour, lol.