[quote=@The Nexerus]
No. You said Diet Mountain Dew was the most disappointing soft-drink, meaning that it tasted the worst in comparison to what you were expecting. You also said it wasn't the worst tasting, so you must therefore have expected it to be good, or at least better than other diet soft-drinks. My question was, why? 
[/quote]

It's not bad tasting. It's drinkable. It doesn't taste bad.

The problem is that regular Mountain Dew is so powerful, and so DMD is a more noticeable step down than, say, a Diet Coke.