In Japanese, ヘッド and 総長 are both used as the title of the leader of (relatively young) street gangs, outlaws, bōsōzoku, etc. Although 総長 is sometimes used also by legitimate organizations, ヘッド is almost specific to outlaws. In this context, the difference between ヘッド and 総長 is not large, but ヘッド tends to sound like the leader of a smaller team, while 総長 is more grandiose and sounds like the president of a larger organization. This may be why this character hates to be called ヘッド, but prideful people want to be called only in one way, anyway.
By the way, we can read all the lines of this character here. Here's an excerpt:
- てってめぇ！ あんなザコと俺のチームを一緒にしやがる気か！ ゆるせねぇ！！
- ヘッ、ヘッド～！？ て、てめぇ～！！ そんなハズカシイ名前で呼びやがって、"総長"と呼べ！
- ぼ、暴走族ぅ～！？ てめぇ…重ね重ね…！！ 上等だぁ、オルァ！
So イノブスキー strongly hates to be called a 暴走族 although he is obviously a reckless motorcycle gangster himself. This reminds me of the "暴走族 vs 走り屋" controversy which is described in Wikipedia. 暴走族 is a catch-all term that refers to various types of reckless motorcycle riders in Japan, but its stereotype is violent street gangs wearing intimidating costumes. On the other hand, a 走り屋 takes pride in being different from typical 暴走族, and they regard themselves as the genuine lovers of motorcycles and street racing. Although many people do not distinguish them strictly, such distinction is important to some. I suppose イノブスキー want others to regard him as not a 暴走族 but a 走り屋.