Why Kitty, why?

So as I am sure many of my fellow cat owners have noticed their feline friends display unusual characteristics. Take, for example, my cat CJ. He is a lovable cinnamon tabby who apparently has no concept of personal space. Picture this if you will, and some of you with weak stomachs should not, I am sitting on the toilet minding my own business. Suddenly a feel soft fur against my leg and before I can even reach down to acknowledge his presence CJ is in my lap and flopping into place to get comfortable. I stared at him for several long seconds before sighing in defeat. Why do cats do this? Thoughts or experiences anyone?