For me there are three biggies
-Waiting for friends to arrive at a bowling alley in Wolverhampton, playing coin-op Crazy Taxi and realising I'd just put £18(!) in the machine and that had been my budget for the evening. Next stop cash machine, next day down GAME to buy a DC.
-Always having 10 or 15 minutes in a morning before needing to leave for work, booting up Volfied on the ST then getting to the point where I was thinking "I can have one more game now if I just drive to work a bit faster".

-Starting a game of Sid Meier's Pirates on the XBox late on a Sunday morning, and then suddenly realising it is now 7:30 at night. Banned myself from playing this now!
Coop