A condition marked by an urge to clear your inbox by batch-deleting all your unread e-mail, regardless of content.
Your inbox is peppered with unread messages going back three months, because you only ever read messages that appear important at the time you're checking. Eventually, you become stressed out every time you open your email and see something like "New Messages (257)." You then have an attack of DELETITIS which involves selecting all unread messages and deleting them, regardless of sender or subject. Now it says "New Messages (0)." Now you're caught up.
On phone: “Sorry I missed the family reunion, Mom... Yes..., I kno... yes, Mom, I know you emailed me the date and time but I had deletitis last week. Yes it IS an excuse... Yes it is... Is too... Is too...”