Coming from someone who likes Red Bull, I can tell you out of code RBs can be really disgusting.

I don't drink sugar free that often, but in my store we had a can kicking around in our cooler and I had it, spit it out and threw it away. I think it got mixed up and pushed back there, but it had to be 3 years old at least.

It was really rancid tasting, I should have checked the can but I was so disgusted I just tossed it.