abbreviation of "Tank Thrash The Gash" a punk rocker saying, usually when something good has happened. unknown what it stands for, who started it, if its in a song or not...
Person : yeah you want to come to this party, there will be hot women and lots of free beer
Person : Tank Thrash The Gash!!
Person : (for not apparent reason) Tank Thrash! (while driving in their car listening to good punk and in the company of mates)