An old school project I did years ago, when I was first learning how to implement Google search into my sites.
This page uses a basic Google site search box, where the search is intercepted by some Javascript, which grabs the term input by the user, adds to it one of several randomly generated "rude" words, and then sends the new search terms off. What the users sees is results for what they typed, plus some other stuff.
See it in action here.