Yes, I have... humorously bought a bottle with a friend after discovering it at a Vitamin Shoppe location. The name, the claims, and the funny accents we instantly imitated all attributed cause to buying it.
It truely is a rediculous product, but I suppose there is the smallest market opening for such a thing. To truely hit the 5000 calorie mark, one would need to mix the entire tub (yes, the entire 20 some odd dollar thing) into a gallon of whole milk, to be consumed throughout the day. If you manage to eat 3 normal meals along with it, you're something else.
Taste wise, if I remember right, it wasn't all that bad! I had half of the container, and after really letting what just happened sink in at the time, I did not even try for the "2500" like we inteded. Almost like a "how many chicken nuggets can you eat" type deal... good times. I used it on and off post-workout, at a rough 30g protein estimate, and back to what I was writing, it didn't taste so bad!