Here are a few of mine...
I've been subscribed to LoveFilm for about 2 years, stopped using it a year ago when I subscribed to Netflix. Not used in 12 months, total waste of 12 months at £7.99 is £95.88.
I signed up for a cycle to work scheme. It gave you tax benefits as you purchased it through work and came off your monthly pay check before tax deductions. Bought a bike worth £660 and got a new job soon after. I did a total of 10 miles. £66 per mile, £660 wasted. Sold it to my brother for £200.
The gym. I signed up for my first year of uni. Went 3 times. £90 gone.
Gym again. I signed up February 2012, went twice, cancelled April 2013. 13 months + sign up £226.
Golf club. I signed up last April. Played 3 times last year due to wedding/house/weather and laziness. Cost me £1,000. £330 per round of golf. Played once this year so far.
Yes, I'm an idiot.