Q: Why was the metal wire so upset?
A: It was getting bent out of shape over nothing!

Explanation: Metal wire comes in all sorts of sizes, measured by how thick it is.  Electrical wire also comes in different thicknesses.  Metal wire can be bent into many shapes so it is useful for art, for wiring a house, making motors, …  When you bend a wire, you can make it into almost any shape

To get bent out of shape is an idiom meaning to get angry.  If you get bent out of shape over nothing, you get mad for no reason.

This joke is funny because it plays with two meanings of getting bent out of shape: the literal meaning of bending a wire, and the idiom meaning to get angry.

Here is some wire getting bent into shape: