a) "You watch Yugioh? Have you graduated from Elementary School yet?"
Reason: watched 4kids version of Yugioh.
b) "Hey, Yugioh is super cool."
Reason: watched Japanese version of Yugioh.
Older yugioh fans no longer talk about Yugioh in public in the U.S. because of the way 4kids has edited out all the cool parts of Yugioh. Cool stuff such as death, violence, and way darker feel of the Japanese version does not exist in the 4kids version of Yugioh, so now everyone in the US thinks it's a show for 6-10 year olds. Until they see the Japanese version.
Wanna screw over an 8 year old and you live in the US? Tell his parents you're gonna have fun watching yugioh and teaching the card game to him. Don't tell them you're showing him the japanese version. Do that for a while, then watch what happens.