A few years ago, I was seated near a lav in the mid-section of a widebody, and could easily observe pax going/in out. A man approached the lav with a rather big paperback book, entered, and remained in there for an exceptionally long time. Mind you, I recall it was a completely full flight.

Several pax waited patiently for this lav, but all eventually gave up and went elsewhere.

How rude.