Around here, it's called the "48 Hour Rule"
Mainly, as a reward for a fellow sneaking new and inexpensive objects into the house and also escaping any female wrath that might accrue from said purchase, the fellow may make up any story he wishes after 48 hours regarding the acquisition.

In other words, she gets 48 hours to notice the purchase and complain. If she misses her window, you are home free.

"This old thing," you might say, when, after a week, she finally does notice, "that thing has been here since July."
( BrokenCoccyx doesn't mind if you grope on, Mon 24 May 2010, 17:12, 1 reply)

^this^
...is chuffing brilliant! I'll let you know how I get on with the £400 graphics card I've just ordered...
(Billy The Fish wants to gargle with Lucy Pinder's bath water, Mon 24 May 2010, 19:36, closed)