Be afraid of the squirrels
I discovered this simple game by accident and it's so addictive it should be banned. I feel like I'm in that bad episode of Star Trek Next Generation called "The Game" where everyone gets addicted to a game (and they have to be saved by Wil Weaton).
It looks deceivingly innocent and cute - various differently coloured squirrels in a grid. You click on a squirrel and all the squares of the same colour that are next to it vanish. You click again and more squares vanish. The goal is to get rid of all the squares. It's nigh on impossible to do this, so when you finish, you immediately want to start again. The other night I started playing this stupid game at 10:30pm and when I next looked at the clock it was 1 in the morning. I can never get that time back! And afterwards, when I closed my eyes I saw squirrels! It's not right.