10. I didn't cut the other guy's deck, and he got Painful, Pot, and Graceful first turn.

09. I didn't know that the set wasn't tournament legal yet.

08. I forgot or didn't feel like Side-Decking. I don't have a Side-Deck.

07. I couldn't play a combo/card because I didn't know the ruling.

06. I never checked how many cards were in my opponent's hand before I played my cards and emptied my enitre hand.

05. I discarded my whole hand to set up for an attack when they have 8000LP.

04. What's priority?

03. I forgot I had Sinister Serpent in my graveyard.

02. I played Forceful Sentry a turn before, and I forgot what my opponent should have in his/her hand.

01. Was the Yu-Gi-Oh tournament yesterday?

Any comments or questions, please address to AzNLeviathan@aol.com
P.S. This was just for humor, I didn't put much thought or effort into this, so don't complain too much =)