What does it mean to be called a "tool?

I think it refers to a guy who is so focused on getting sex that he’ll do any damn fool thing if he thinks it might result in getting an orgasm for himself. There are some women who will exploit this.

Nothing good.

This UrbanDictionary definition about sums up how I’ve always used it: Someone whose ego FAR exceeds his talent, intelligence, and likeability. But, of course, he is clueless regarding that fact. He erroneously thinks he is THE MAN!

My how things have changed. It used to mean penis.

It means the same thing as jerk, asshole, and douche-bag.

Look in a tool box.
Everything in it can be used, but can’t do anything on its own.

As @lucillelucillelucille says, It’s slang for penis.
So as insults go, you’re calling a guy a prick or a dick or a tool.

A ‘means’? in one sense. Or in another sense a ‘dick’

Someone who, often unwittingly, is used to carry out someone else’s designs.