Almost forgot this one, which is strange considering how often it came up in discussion between people I used to interact with somewhat regularly.
Brawndo, the Thirst Mutilator:
https://youtu.be/VBML3VpbuYQ Of course, a company did make actual Brawndo eventually. One of the people I mention managed to get a can and his assessment of it was "it tastes like SweeTarts in a can".
Some of the other ads in Idiocracy are pretty funny as well but they're more along parody than they are fictional due to the fact that they just riff on actual real world ads (Carl's Jr.: "F**k you, I'm eating!", etc.).