Tank Girl's pants and legwear are pretty open to interpretation. We've often seen her with tall socks and ripped stockings, workout shorts, cutoff jeans, baseball pants, and chunky lettered belt buckles.
Use what you can find and try to anticipate the weather for your occasion. You can also add details like dirt, bandages, knee pads, garters, etc.
Use a pair of faded blue or grey jeans to make a pair of cutoffs. Put the jeans on and draw a line with pen or marking chalk about 1/4" lower than where you want your cutoffs to end.
Continue your line around the back of the jeans. Take the jeans off and cut around the lines. The front and back will not be symmetrical, so don't try to cut straight across the whole pant leg at once or you'll end up showing more cheek than you intended.
Use sandpaper to rough up the edge of the cutoffs or, if you have time, run them through the washer and dryer to fray the edge.
The right boots are essential for this costome. A lot of other features can withstand plenty of artistic license, a pair of iconic combat boots are mandatory for Tank Girl. Pictured above are the Kathleena Strap Calf Boot by Dr. Martens.