The worst ever decision I made was losing the private keys to one of my online wallets. I didn't had a backup, and all the coins are now gone. I tried quite hard to retrieve the coins, but it is of no use.
I also wanted to do this, but the fear of loss stopped me. Now my coins are safe.
I once sold 5btc at rate $400 then i spent to get drunk with friends, because i was depressed. This is really a very bad decision