Yeah, some days ago I wanted to plug the audio-cable of my portable speakers into the MP3-player. Instead I stuck the speakers' DC-adapter into the audio-jack of the player... same form factor, same size, I wondered why the player behaved a bit irritating... fortunately the jack only had ground on the outside. Lesson learnt: Don't plug cables without even watching.
Lesson learnt: Don't plug cables without even watching.
The real lesson to learn is one of design - don't design your products so that power can (potentially) be plugged into signal, and vice-versa. Similarly, each connector that performs a particular function should be standardized to that function only; back in the day, DB-9 connectors were standard for a lot of functionality on a PC; CGA/EGA were female DB-9, while serial ports were male - then somebody got enterprising with M-M/F-F adapters - and sparks were born!