If you like this movie....
You should be happy that Tropic Thunder coined the whole "Never go full retard" line. I bet you that tons of people who would have never heard of "I Am Sam" are now aware of it's existence.
Hell, I didn't know about "I Am Sam," but now I am actually kinda curious about it. I really, REALLY want to see what going full retard is all about. I would have never in a million years considered seeing this movie if it wasn't for "going full retard." And I am sure there are a lot of people just like me.