Everyone has a retard thing. A retard thing is the lack of knowledge of a fact or bit of wisdom that is so utterly common it makes others laugh with scorn when they learn it has passed by their conversation partner.
The retard thing lurks in the recess of the brain, looking for its baseball, waiting to strike an unsuspecting victim. Sometimes the retard thing is so pervasive that it returns even after the initial slip up, further haunting its victim.
My retard thing is that I often confuse the word animal for the word mammal. I don't know why I do this and it invariably draws the ire of my conversation companions but I'm still always hesitant to use the word animal when referring to fish or reptiles.
Another example - within the fish er animal kingdom - a friend thought that tuna was the food name for dolphins (eg. venison; deer). (Aside: this was my friend Miguel Bonaparte, who said this while actually eating tuna, I love the fact that animal activists are all up in arms about tuna fishermen catching dolphins in their nets and not releasing them while Miguel actually thought he was actively eating dolphins).
Other examples include: A person who thought "soap operas" were called "sobapras"; a person who thought that Costa Rica was an island until a year ago because it's name sounds island-like; the common misconception of "intents and purposes" for "intensive purposes"; etc.
Two other notes:
Anyone familiar with Nip/Tuck or the OC is familiar with AnnaLynne McCord the young sexpot placed on both shows to stir up controversy and frustrate aging virgins. What those familiar with her may not know is that it is very, very difficult to find her age on the internet. (If you want to try for yourself, go now, I'll wait). It took me nearly 30 minutes before I came across this link which puts her age at either 19 or 20 years-old depending on her birthday. I find it to be really interesting that her or those that represent her (or Nip/Tuck) have gone to such great lengths to disguise her age.
And finally, congratulations to my New York Football Giants for setting the NFL single season record for most headlines that employ the word "escape" when describing victory. We couldn't be prouder fellas.