When I was about twelve, I went out with a friend from school to a shop nearby to see what we could get. We bought a few random things, like a load of eggs to play "eggball" with, as well as your typical two litre bottle of coke.
Only this was Co-Op Brand Coke Substitute, or something along those lines, and the cost came to the grand total of 25p. I had one sip. It tasted as good as it sounds, and we did end up pouring it down a drain. In a way sipping a 25p two litre bottle of coke is something everyone should try, but me being me at twelve, I was expecting the usual taste, not something that tasted as though it had been mixed in a football stadium men's room urinal.
I'd never heard of the Coke Blak, but I've got a bit of a weird taste in my mouth now while I try to imagine a Coke-coffee hybrid... this is going to keep me up all night.