How can I make my own mad gab phrases?

I hate to say this, but I don't think there is. I've just done about five google searches to see if I could find anything, but alas, there is nothing to find. There are however a few nifty sites where you can play madgab (i.e. guessing ones that have been posted on the site) try typing "Mad-Gab" into your favorite search engine next time you get a chance, it could be worth a larf or two if you have some spare time on your hands.