I think this would work better as a dressing room than an actual RPG, but I did this briefly with some friends and we had a great laugh at how awful they were.

The icing on the cake was the fact that our storyline itself was semi-serious and we attracted a few genuine Sues (they hadn't seen our ridiculous character applications before apping and there was nothing in the rules that invited Mary Sues). Because everyone was a Sue or a Stu, though, we all had fun while it lasted. What was absolutely hilarious was the fact that one of the unintentional Sues managed to be more of a trainwreck than our deliberate Sues/Stus.