So far, the only unexpected boarders were in Riga, Latvia. I heard people on the fore-deck and thought my friends had returned. but 20 minutes later, with no words from them, I emerged from the engine room (doing what I do best, changing fluids) to discover a wedding couple were taking wedding pictures on deck.
Wifey B: Once had alarm go off when away from boat at marina and pulled up the cameras and saw a young couple about to have a make out session on the seating in the aft area of the cockpit. I spoke to them through the speaker and then told them to just continue as they were but not to go elsewhere on the boat. Of course knowing I could see them made them a bit more shy so they just sat and talked and kissed a little.