They didn't actually show Marcus though, it was funny because the other housemates knew what he was doing and embarrassed him.
Alex Sibley wouldn't be pleased, he had a meltdown over people peeing in the shower. Don't see the problem myself, if someone I was sharing a house with had to masturbate I'd prefer they do it somewhere it can be easily washed away rather than on a towel or something I could be in danger of using.