when you put excessive pictures of old people (particularly grans, if it is a males possesions)somewhere hidden for someone to find at a later date. usually in a possesion which wil be carried around, such as a wallet.
The pictures are usually small so that they
will not be found until embarressing moments (see example). Also quite commonly cuttings from old peoples magazines or adverts.
guy 1: dude, i totally gran spiked you yesterday, i cant believe you didnt find those pictures in your wallet until today!
guy 2: yeah, i was mega embarressed, the woman serving me at the checkout gave me well dodgy looks when those pictures of grans flew out my wallet when i went to pay, so thanks for that!