Whenever I display my Global Inbox, the top item is always a recurring event we have for the StackExchange Game-On! event set for every 21 days. It is also highlighted as if it were new if there are any other new items in the Global Inbox.
Sorry about that; this was a combination of two bugs causing this (under pretty narrow conditions).
This shouldn't happen again, and those items should disappear from your inbox later today.