Unfortunately that is not slang for great, it literally can make you blind.
On the 15th July 2011 an explosion in an illegal distillery in Boston, UK, killed 5 men and uncovered a £1bn fake vodka scam. In the same month, another distillery located on Brewery Street, Birmingham was raided and fake vodka containing dangerous levels of methanol were found.
So how is it faked? There are a number of ways to adulterate vodka: add water, repackage a cheap vodka in an expensive vodka bottle, or the most dangerous, distill ethanol (drinking alcohol) from industrial alcohol (also contains methanol). The biggest problem is that in general methanol is still present after distillation at levels that can cause blindness, kidney damage or even death.
Basic rules to spot a fake vodka? If the price looks too good to be true, it probably is…