Worst Five:
1. We're all living in America, America is wunderbar...
-In the first episode, Kaiba refers to himself as the Japanese champion. When being welcomed to Domino, Ishizu is told, "Welcome to America!"
What is the Japanese champion doing attending high school in America? Our standard of teaching sucks compared to Japan! (Apparently, Domino City moves between countries, because later they talk about going to America during Waking the Dragons, and it was made quite clear they needed plane tickets to get back home. The only explaination for that, if Domino was still in America, is that it's in Hawaii, and somehow I just don't think it is.)
2. Yugi, let me help you!
-Up to that point, it was pretty clear that Atem was doing the dueling when Yugi's eyes went all slanty. Changing that episode, so that Atem was supposedly being held back, instead of in need of Yugi's skills, threw the entire thing into confusion.
3. The Magic Marker.
-Dubbing out women's chests. I have an entire article about this at my Horakte's Sock Drawer blog. My body is not a corruptive force, and neither is Mai's, no matter how low her neckline is, as long as she's still actually clothed.
4. I miss you, Kaiba.
-(sputter) Mokuba just called Seto by their ADOPTIVE SURNAME! In one of Seto's FLASHBACKS! From BEFORE they were ADOPTED!
5. After our parents died-- I mean disappeared...
-In Duelist Kingdom, Mokuba and Kaiba both clearly say their parents passed away or DIED, respectively. During Noa's storyline, the policy on death had been changed, so Kaiba had to say they had "disappeared," clearly contradicting earlier dialogue. The only way to explain this away is that previously, they'd been talking to themselves, and so apparently Seto and Mokuba don't say the truth of what happened to their parents in front of each other?
Best Five:
1. "You can beg later. When you are punished." "Huh!?"
-Every single time Pegasus suggests locking Croquet away or torturing him, Croquet responds in the most bewildered tone of voice, like he has no idea what the hell Pegasus is talking about. It's hilarious.
2. "No I refuse!"
-Invid and I quote this at each other sometimes.
3. "You'll pay for that stinging jab with your life points!" "DUEL!"
-This too.
4. "When that blade touches your legs, it'll send you straight to the SHADOW REALM!"
-My soul is in my LEGS? Bahahahaha. No, no, what does it really do?
5. Pegasus's favorite fruit juice.
-Oh come on, like little kids don't know grown-ups drink wine. It's better than what Daddy probably drinks. It even has health benefits. And anyway, shouldn't it be GOOD to show the bad guy doing something you don't want little kids to do? He's the BAD GUY.
I find most of the other really weird stuff in the dub fairly easy to ignore, actually. It mainly amounts to looking elsewhere on the screen, or closing your eyes for a few moments and thinking about butterflies. XD
Obviously, this is all a matter of opinions. But it made ME laugh.