As an adjective describing behavior:
* His decision to quit his job without a plan was completely irrational.
* The fear of spiders is a common, but irrational, phobia.
* It's irrational to think that you can control the weather.
As an adjective describing numbers:
* Pi is an irrational number, meaning it cannot be expressed as a simple fraction.
* The square root of 2 is another example of an irrational number.
* Mathematicians have proven that irrational numbers exist, even though they cannot be precisely represented.
As a noun:
* His fear was based on pure irrationality.
* The study of irrational numbers is a fascinating area of mathematics.
* The argument was filled with irrational claims and accusations.
In a figurative sense:
* She was consumed by irrational jealousy.
* The situation was becoming increasingly irrational, with both sides refusing to compromise.
* It's important to step back and analyze the situation logically, rather than letting your emotions lead to irrational decisions.