What are some the more idiotic and stupid mistakes that you know you shouldn't have made but did anyway. Yes this includes other none gambling stuff like sending btc to the wrong address. I'm interested to find out the stupid things other people do. 
Actually I made never such type of mistake in my two year Bitcoin carrier . Since one of my friend send me Bitcoin with custom trader charge of 0.01btc . I think there can be no big mistake than to pay a transaction charge more than the amount what you need to pay .