• The title itself is word play. If you happen to be or were into the Jrock or Visual Kei scene you may already be familiar with a lot of these words.
• It's a combo of Headbanger and Band Gal. A band girl is a really dedicated fangirl who goes to a lot of shows and dedicates much time/$ to the band she likes. Such as you see in the video with the framed band photos, further implying.
• 15 gets pronounced like saying "One Five" in English instead of juugo. Not sure if done that way to fit the melody or a dual meaning....
• ドセン is dosen. It's center stage. Really hardcore fans or fans who really like the vocalist will aim for this spot. Very competitive.
• 逆ダイ is Gaku-dai. A type of headbang where you like bend from the waist down and come back up. Think something like a bowing-headbang.

At 4:50 you can see this here http://youtu.be/QOkpVhKgQlU?t=4m50s or here at 1:02 http://youtu.be/8YnBqdfmJg4?t=1m2s You do it to the beat most the time.

• 柵ダイ is Saku-sai. Pretty much just crowding up to the fence that blocks you from the stage.
• コロダイ is koro-dai. The equivalent of crowd surfing. But generally in Japan I think this mainly done by the members of the group than random crowd people.
• 狂い咲く literally is "late season bloom" BUT holds a secondary rock music meaning. For the lyrics I left with it's meaning but how it's done live I'll give example. You like wave your arms and create a ~blossom thing~ and then keep doing it.

Flow-y thing hands the whole crowd intro http://youtu.be/m7Zp1Ukrts0?t=1h13m37s

• "nakimushi na YATSU wa koko kara kierusero" the yatsu is a very derogatory way of saying "you". I didn't know how to express that without swearing but I didn't want to put swears where they technically never were. English doesn't really have an equivalent?

(omg this VK stuff really brought up all my 14-16 years old memories too, thanks Babymetal.)