The rules of this ongoing bro-focused prank/lifestyle are simple:
“Buy Smirnoff ice, present it to one of your bro’s in any manner, your bro must instantly get on one knee and chug the Smirnoff ice on the spot regardless of setting.
“1) You cannot refuse an ice. If you refuse to drink the ice you are instantly excommunicated and shunned, and thus can never ice another bro or be iced.
“2) If you are iced by a fellow bro you can ice block. When presented w/ an ice, you pull out an ice of your own and reverse the ice on your bro. The ultimate ice insult.”
The fun comes from presenting Ices in creative ways and in inappropriate places (to a runner who has just finished a 5K, to a dude on his way to church, to someone testifying at a Congressional hearing on the civilian death toll in Iraq, etc.) and from, apparently, presenting room-temperature or warm Ices of particularly off-brand flavors including mango and grape.
Further reading: urlesque interviews the creators of the phenomenon, who share some cool Icing ideas (Icing people driving cars is a particularly great choice), and the spin-off site Ices Icing Ices (featuring Ice Cube, Ice-T, Vanilla Ice, and so forth).