Boomboxes.
I suppose it doesn't matter at a crowded beach, since that is the occasion of social gatherings. but it never ceases to amaze me that idiots can't leave civilization behind when venturing into the wilderness. When I visit the wilderness, I enjoy the sound of water rushing over the rapids, the wind blowing through the trees, the chatter of the wildlife. Then along comes some moron blasting his moron music.
And littering...oy!