The one ingredient in this that I know is the culprit would be Guarana seed extract. I have a whole tub of gaurana and it tastes like bitter dirt, which is the exact flavor I'm getting from this. Also it's the 4th ingredient so there's definitely enough to ruin the taste. It tastes like 1/2 dirt 1/2 peach 

I have zero clue why they wouldn't just use just coffee bean or green tea for the caffeine. They use a mix of gaurana, green tea, and synthetic caffeine for a reason I do not understand. 

They could use any other caffeine formula and it would be better but for some reason they used gaurana which has the worst taste of all of them.

For clarification I also did not buy this drink, my gf gave it to me because she bought a bunch and didn't like it, so even the "free tastes better" doesn't apply here. I shall finish it for the caffeine but I will not be enjoying it one bit.

This is in every celcius flavor so I'm not sure how people don't notice this taste or maybe they just haven't had drinks that don't taste like this, like Ghost, Alani, Gorilla Mind, Monster, Redbull, Bum, Reign, Bang, etc (literally any other drink) and think it's normal

TLDR; It tastes like dirt because of Guarana seed extract 

This drink tastes like they threw bitter dirt in it - 1 ingredient explains why