When someone tries to always outshine you.
I climbed mount everest without mount picks or a jacket. What am amazing feat for me!
Thunder Thief would say to everyone "Oh yeh, i did it without shoes, food or oxygen!"
You would say something like this to a group of your friends "I made the best cookies today."
Thunder Thief would say "Whatever they were total garbage. They were crusty and gross."
Reply: You are such a Thunder Thief.
"Ha! Yeah, that punk is such a thunderthief."