... IMO the correct behaviour of a maintenance man when intending to do something like this but realizing you´re in the showr would have been knocking at your bathroom door til you reply and telling you what he´s about to do. Or coming back later if you failed to reply (e.g. because you didn´t hear him under the shower.
Now by his behaviour the guy was practically begging to be attacked. And he was lucky your weapon was a bottle of shampoo. Living in a country where it might well have been a gun, this dude is a sure candidate for a Darwin award.
I'll be more enthusiastic about encouraging thinking outside the box when there's evidence of any thinking going on inside it.
(Terry Pratchett)