No, it's not April 1st. No, Mario hasn't suddenly turned into a serial killer. Employee's of UK retailer GAME are reporting an email sent around stores just before closing to remove Mario Party 8 and all applicable advertising due to the game having an "offensive" word, details of which can be seen in the screenshot below.
It's not clear if other retailers will take the same stance as GAME, but it is worth mentioning that Mind quiz also suffered the same fate last week for the exact same offensive word.
With no official word from Nintendo or GAME, we'll keep you updated on the news.
***UPDATE***
We've just received word of a Nintendo statement;
The above game was launched in the UK today. Unfortunately we have discovered that a small number of games contain the wrong version of the disk due to an assembly error. We have therefore decided to recall all copies of the game from UK retailers so that this mistake can be corrected.
We will re-launch Mario Party 8 in the UK as soon as possible and will announce a new launch date shortly. We very much regret any inconvenience caused.
Employees of British video game retailer GAME are reporting an email sent around stores to remove the popular Wii board party game ''Mario Party 8'' and all applicable advertising due to the game having a word considered to be offensive in Britain.

The word is "spastic," and can be seen on the "Shy Guy's Perplex Express" board. If a player lands on one of several certain green spaces, Magikoopa will appear and, before rearranging the train cars, will say, "Magikoopa magic! Turn the train ''spastic'' Make this ticket tragic!"

Nintendo is currently developing an updated version of the game without the offending word.

This is not the first time a video game has been banned in the UK for including the word "spastic." Last month, Ubisoft announced a recall of its PSP brain-training game ''Mind Quiz'' after a mother of a child with cerebral palsy complained because the game called her a "spastic" for not doing well.