Rule 5?
When you gotta' go, you gotta' go... but:
Nap Time, a recreational cruising boat, runs into the starboard side of a huge Washington State ferry going from Tacoma to Vachon Island in broad daylight.... it turns out, according to a local TV station, that Nap Time‘s captain, the only person on board at the time, was below, using the head.
Rule 5 of the COLREGS requires that all vessels, shall at all times, maintain a proper lookout. That's why some towboats have a head in the pilothouse. That said, there appears to be room for debate concerning the give-way status in this case. I'm not going to enter that debate because I'm not familiar with the conditions surrounding this incident. But, it's a well known fact that nobody can use the NAVRULES to justify a collision, and there is certainly no justification for ignoring them.
When you're on autopilot, doing your business in the head, with nobody on the helm, hearing 5 short blasts from a 250Hz horn close off the bow is probably more effective than exlax!
/fl