Someone posted a picture of one, but no link
Small bluetooth speakers for bicycles - Buckshot | OutdoorTech
I use this everyday. I dig it. As for annoying other cyclists, I rarely see any other cyclists. This speaker has buttons that allow me to control the music. I can pause my music when around others or at least turn it down.
It also has a mic, so when bluetoothed to my phone, I can take calls (well, sort of). The wind on the mic makes having a conversation kind of impossible, so my reply is usually, "I'm on my bike. Let me stop and call you back."