I think UnderneathTheWaves summed it the best (forum #46161), but more can be done to really clear up the tags. Obviously as mentioned in the Yankee wiki it is for both genders, but if one outweighs the other in a certain medium I usually go with it. So sorry if the wiki prevented anyone from adding other images, I didn't realize it was that off putting. How about starting fresh with the wikis mentioned and deleting them, then specifying, danbooru wise, what images should be sorted under each tag.
For the images currently under the mentioned tags, how about tagging all of them under delinquent or gang so they will be reworked for sorting. It will be tedious to sort the images if they are under each and we currently have no image guide to work with.
Bousouzoku - Should be the main one in use, but what depiction do you guys want to go with, the caricature type? A female bousouzoku in a skirt is odd imo, but I guess if it is portraying the stereotypical look (like a costume) then it seems to be alright. jumpsuit, pompadour, motorcycle, bandages, bokken??
For example post #145895, post #703215, characters doing the squatting pose or standing pose and holding a bokken but is not dressed as either bousouzoku or yankee... should it be bousouzoku_style / bousouzoku_pose?
Yankee - Should be the one under delinquent. School uniform wearing trouble makers, so make the wiki more obvious that it is both genders. gakuran, serafuku, bleached hair, bouken??
Banchou and Sukeban both seem to be used specifically for leader titles, so unless the leader is obvious, the tag doesn't seem to be of use. In at least one image there is someone with a bouken... does that defy the leader (or side man) if you can see no title on their clothing?
Ouendan - All the images are correct, no clean up needed.
Gangster -> mafia / yakuza