Some important context here is that this is an effort to deal with terribly behaving British tourists, since the same bylaw also bans walking around nude or only in underwear. In addition to just being terrible tourists generally, there’s a history of British tourists treating Spanish beaches like their personal vacationing grounds and not a different country where other people live and speak a different language.
Debtor's prison is pretty much universally considered a violation of basic human rights. In the US there is even a strong contingent of legal scholars who feel that cash bail cannot be justified.
I apologize I don't have time now to find a source for that.
A stag do is the male equivalent. In the UK & Ireland the word "do" is used often for social gatherings or events. Like a "work do" means you're going out for drinks or whatever with colleagues from your workplace.
Now picture in your mind that, again, and again, and again and it's now the 20th time this month.
There are no cool things that cannot be spoiled by being done all the time, relentlessly.
Also in my experience - having lived in Britain - the brits doing this stuff actually behave even worse outside their own country than in Britain (which is quiet shocking if you're familiar with Friday and Saturday nights in areas like Essex) - British hen and stag dues are expected to be extreme nowadays and they get worse when abroad in the kind of place that's just a cheap flight away from most of Britain and is comparitivelly much cheaper, because the kind of Britons you get there couldn't give a rats arse about what foreigners think (Brexit didn't happen in a vacuum and the whole idea that "Brits are superior" is definitelly common in Britain, especially England) so their behaviour abroad is even more unrestrained than in their own country and not just in this kind of dress-like-a-cock way (which IMHO is fine, even if it gets old after a while) but they're very loud at all hours of the day and night, and prone to fights and breaking things.
(In the context of Europe, Brits are pretty bad in how they handle drinking since they're prone to binge drinking rather than having habitual moderate drinking - such as normally having a beer or a glass of wine with lunch - so not only do they really go for getting drunk as fast and as hard as possible in those traditional two days a week of going out and getting pissed but also, funnilly enough, by not drinking in a moderate way the rest of the week they don't have the same capability of handling their booze as many other Europeans)
I suspect what they did in this town is more some kind of half-arsed pushback against that more general behaviour problem of loudness, rowdiness and destructivness than the actual costumes, only in trying to balance the interests of the hotel and bar owners with those of the people who do not make a living from the cheap side of the Tourism Industry, they came up with this "trick" to try and make it less appealing for hen and stag dues or at least for the ones with the more rowdy crowds.
No Bucks/Hens nights was one of my rules as a pub bouncer. It's always trouble. It's mostly a group of friends out for a piss up and extremely bad behaviour at the expense of other patrons enjoyment.