Tool

When someone calls you a tool, it means they think you're being a big ol' jerk. Most often, people use this insult to call out an egotistical male for acting like a douchebag.

In the past, tool was more commonly used to refer to a person who others can easily manipulate (like a mechanical tool). However, as tool became synonymous with a certain piece of male anatomy, it also became synonymous with males who act like that piece of their anatomy. This is how tool became a term used to describe toxic, stupid, overbearing, and/or insensitive men.