I reached over and touched the plug-in and it was smoking hot. No visible signs--no smoke or glow. It was fully engaged and not corroded. It was not at full load--only about 14 amps on a 30 amp plug. In fact, I don't leave the boat plugged in--I used solar for charging and only plug-in when I'm there. And the end I move is the dock end (this is the boat end).
So, yes, it can happen in a heartbeat, and I'm glad I was there.
(not my picture--I pitched the plug in my haste and horror--but I can't see anyone minding repetition of a safety reminder. The extent of damage was very similar.)