When you did something stupid and then forgot (or pretended to forget) about it. Fortunately, your local support group (AKA "friends") will be sure that epic tales of dumbness are regularly resurrected at parties, family reunions and all other social gatherings, even in your absence, so that such tales are added to the collective consciousness and, thus, are never truly forgotten.
Ann experienced dumbnesia when she forgot about the time she set the microwave for 30 minutes instead of 30 seconds. Fortunately, her fellow residents in the dorm remind her at every gathering.
by xcici October 11, 2010