In Ruby, I didn't know how to get past the guy in Oldale being like I SPOTTED A RARE POKéMON'S FOOTPRINTS!! for a day or two. Then I realized that I was supposed to fight Brendan. XD
And then much later in the game, I couldn't defeat the Elite Four on my first try. My solution? Grind my team to level 70 (somehow. I'm still puzzled by this because it's HARD AS FUCK TO GRIND IN RUBY PRE-E4) and fight it with half of my team "borrowed" from my sister. XD;;; Might not be as uh... 'bad' as the other posts in this thread for the lack of a better word, but it's the only thing I can think of other than some of my Platinum moments.
If GenIV is included.. well, I was kind of playing through it barely knowing any Japanese... so when I beat Byron's gym it took me like an hour to realize that I was supposed to get Strength at Iron Island to get Jun to let me in the library. <_< >_> The disadvantage to playing Japanese games before the US release. THERE'S ABSOLUTELY NO INFO FOR ANYTHING. Seriously, playing through Platinum for the little things was fucking hell because there was so little info on it. ;;