I will admit, I expected to hate this movie. And I did at first. Johnny Knoxville is not exactly a person I admire on principal - and it takes a little while to get to the good parts of the movie. So, my best advice is just to stick it out. You'll be kinda glad you did.
The story is far fetched, but most comedies are. Knoxville plays a man named Steve who desperately needs to make some money. He enters somewhat reluctantly into a hairbrained scheme with his crazy uncle to fix the Special Olympics. Pretending to be "Johnny" he enters the compitition. Long story made short: there is a girl, a counselor of sorts, he is found out by some of his other competitors, and they decide to help him.
You don't watch this movie for the romance, the acting, or the meaning. You watch it because of the writing. There are some hilarious one liners in there. Its one of those incredibly quotable movies - "Ice Cream? When the f*^#k did we get Ice Cream?"
I give it a solid 3 and 1/2 stars.