So much rides on a 30-minute job interview, especially if you really, really want the job. Because it is essentially the gateway into the good life (money! electronics! fancy cars!), it is only natural to accidentally let your inner idiot shine when you're operating under so much pressure.
One wrong answer, and you're out. There are 100 other perfectly qualified applicants that could take your place. So at least try to avoid unemployment by not making one of these unfortunately common job interview mistakes.