Didn't have a big yacht, but Daddy had sailboats growing up and we spent a lot of time at Watergate yacht club. These were 40-55 footers, so nothing like a big party yacht.
It wasn't a snooty crowd, by any means, but there are unwritten rules that are born out of tradition and respect for boating, sort of like with golf and polo, and no jeans while playing.
When it comes to commercial party yachts, the rules are likely a bit different. There are personal yachts that size, so just be safe rather than not. 4951