Fake Item Boxes are recurring weapons in the Mario Kart series. They pose a threat to everyone on the course unless they have a star or Bullet Bill. Fake Item Boxes resembles regular Item Boxes, but have a slight shade of red to them, and the "?" mark in them is upside down. If placed in the right place, anyone can easily be fooled into hitting them thinking that they are real Item Boxes. If you are hit by one of these, you flip and your kart stops.
If you are playing on multiplayer, or on wi-fi, you can strategically place your Fake Item Box inside a real Item Box so that some other poor sap runs into it with no clue how it happened! This perfect placing takes practice, and experts have figured out how to know when there's a fake one inside. There is also a VERY easy way to know where a fake Item Box is. You simply look at your map on the bottom screen when you are approaching an Item Box, and if it's a fake one, then it will appear dark red, and if it's real, then it will be a light shade of blue.
In Mario Kart: Double Dash!! and Mario Kart Wii, trying to think they are fake or real is extremely easy and can be easily recognized because they are dark red with black spot rather than being blue, cyan and green. They also have upside down ? mark while real ones have their marks right way up. They just look like real ones, but knocks you out when you accidentally bumped into them.
With Mario Kart 7, they are no longer items