Thinking inside the box 

Take off on an overused board room expression, only this one actually has some actual meaning. To think inside the box simply means to have your mind on sex.

Dude, that board room meeting with Hal & Tom was so boring...they kept talking about thinking outside the box all the while while I was thinking inside the box while staring at the copy girl.

Thinking inside the box by Bangboy July 13, 2009