Definitely a stretch, but for any Futurama fan...

>!It could be Slurm!
Here's a link with more info about it.

I am a food you'd never find or certainly wouldn't eat

>!Of course we can't find it because it's fictional, but even if it were real, I would never eat secretion from the anus of the Wormulon Queen

I don't exist, and yet I do, now isn't that a feat!

>!It doesn't really exist, but does exist in a fictional show

I am a good example of something that is wrong

>!Slurm is a good representation of real world soft drinks and show how corporations promote them even though they're addictive and bad for you

I'm mentioned in the speech of some but more often heard in song.

>!Slurm sounds like slur, which is something some people do when they talk, but usually slurring is intentionally done in songs.

I know it's probably not the answer, but still, food for thought ;-)

Definitely a stretch, but for any Futurama fan...

>!It could be Slurm!
Here's a link with more info about it.

I am a food you'd never find or certainly wouldn't eat

>!Of course we can't find it because it's fictional, but even if it were real, I would never eat secretion from the anus of the Wormulon Queen

I don't exist, and yet I do, now isn't that a feat!

>!It doesn't really exist, but does exist in a fictional show

I am a good example of something that is wrong

>!Slurm is a good representation of real world soft drinks and show how corporations promote them even though they're addictive and bad for you

I'm mentioned in the speech of some but more often heard in song.

>!Slurm sounds like slur, which is something some people do when they talk, but usually slurring is intentionally done in songs.

I know it's probably not the answer, but still, food for thought ;-)
Also, the title says an "Imaginary Food" riddle.