PeaBese said: Anyone knows if there will be such an event somewhere this upcoming summer?
Maybe? Improv Everywhere tends to do different things in public for shock value. So it's very unlikely they will do it every year. More likely a small group of WAMmers/sploshers would do this.
You could always try and start an event. Perhaps pick a day on a weekend and encourage anyone that will be at the beach to all do it the same day. If enough people in different places do it, maybe it would catch on like "underwear day" or something.