In Tundra Express there is the challenge called, "What's Yours Is Mine," where you have to destroy 5 of tiny Tina's pink mines.
I have yet to find any of these ! Where are they located ?
The Borderlands Wiki has a list. If, like me, you find their descriptions somewhat lacking, here is a video demonstrating how to get them.
Till now i only found out 3 of them, one near the bridge leading to end of line, another one is between varkid's spawn and tina's place(right side of the map). The third one is on the top of broken roof/platform.
How to find those first of all they are pink in color(There are regular mine bombs and these), and if you look carefully you will find a green lever on it.
So I found it how to defuse them ? Well as its a proximity mine which is equipped with motion sensor so if you run to it it will explode. The best way to disable those mines are to crouch and move very slowly once you are near the lever just pull it to disable it.
once you do it you will hear something funny from Tina.
On the mission "Mine, all mine" instead of going in, head all the way to the left by the gunner warning tower. After you kill the varkids and the house of bandists, you'll see a pink mine.