Artistic Age: According to Word of God, Tetsu is 17/18, but looks like a middle age man, lampshaded by Emi in Episode 78 when she calls him "Ojisan" and towards the end of Asia-Hen with Ali doing the same.
Dueling Shows: With Yu-Gi-Oh! ZEXAL, which aired the season after it. Both focus on middle school aged kids and card games. It helps that the creator of Vanguard actually started out as a manga-ka for Yu-Gi-Oh! R and Takahashi's (the creator of YGO) understudy.
Fan Nickname: Asaka is called rule 63 Aichi due to their physical similarities.
YandereAichi started to catch on after ride 44. Also PsyAichi.
Among his Japanese fans, Ren is often referred to as "Ren-sama".
Platina Ezel is frequently referred to as Pretzels or PEzel for short.
When Kai shows off having Psyqualia in the manga, it was quickly given the nickname Kaiqualia.
A real life example, Izumi Kitta, Misaki's voice actor, has a tendency to pull two triggers to break through her opponent's guards, and a lot of them are double critical triggers. This has earned her the nickname of Izuqualia.
Like the Gaang and the Krew, Kai and his friends who are looking for Aichi are called the "Mates."
No Export for You: All 3 3DS games, Ride to Victory, Lock On Victory and Stride To Victory. The company that produced the games, Fu Ryu has said that they have no intentions of translating the games. The 3DS region lock doesn't help the matter either. So if you want to play the game, you have to buy a Japanese 3DS just to play it. This has prompted fans to send petitions to Nintendo to localize the games.
The Legion Mate arc of the anime was skipped in the dub. This is due to either Bushiroad wanting to have the dub of the anime and English card releases closer to the Japanese releases, or because of the director for the first 4 series, who also helps with the directing of the dub, retiring.