vmz stands for Vai maicho, zabiese!
Literally it means Oh mommy, my teeth!, but it is used as the Bulgarian equivalent of omg
or better omfg
The phrase originates from villages in the Rodopi mountain. And could be heard when a peasant is astonished at something.
In modern days it may be used by gamers just as synonym of omg
1. A peasant: "Vai maicho zabiese! Penke, the bull has enormous dick
2. Shmendrick, playing Starcraft Broodwar, just lost all his troops again. On the screen appears:
Shmendrick: vmz!! gg