I've had two memorably bad ones-
2008-2009 Spring BR w/ ROTOM
Had a good list, but lost my first game due to my sleepiness and my opponett playing Eeveelutions was using Leafeon(RR) 2nd attack instead of first attack, would've won but i flipped tails on SSU. Ended up 2-2 that day.
2009-2010 Autumn BR w/ LUXAPE
So after being in T40 for the whole season (In seniors, rating of 1618.XX+, yes i know that this was early but it was cool) and 4 consecutive 3-1 one tourneys w/ LuxApe and GeChamp, on this day out of 9 nine players
1 n00b
1 LuxApe
1 Gengar/Aerodactyl
6 FlyChamp
Needless to say I ended up 2-2.. and well never recovered cuz after that all my decks started giving me bad starts....
My worst tourneys though were at Cities with Dialga/Garchomp...