Taste is subjective, of course. But, according to the subreddit r/crappyoffbrands, when it comes to the worst store-brand soda, Clover Valley's MTN Explosion (which is a Dollar General brand) takes the cake.

"That stuff is Awful and tastes nothing like real Mountain Dew!" reddit user Degoragon writes. "DG 'Clover Valley' off-brand sodas are horrible! [They're] even worse than that awful stuff Dollar Tree used to sell in the 'three-liter' bottles that were half Aspartame (NutraSweet), half HFCS." Another reddit user commented with just one rather descriptive word: "Craptacular." 

Following this rant, Degoragon did give a shoutout to one store-brand soda in particular: Sam's Choice, the makers of Sam's Cola. So, there you have it. Imitation Mountain Dew is apparently a no-go, while Sam's Cola could have the potential to trick your friends into thinking it's real Cola during a blind taste test.