When my friend and I played, the first one we got was the crazy ticking clock. We just left the bedroom and heard distant ticking. The clock was literally the last place we looked, because we couldn't figure out where the hell it was coming from. I thought it was pretty crazy, though.
From there, there were a few that blocked off imporant parts of the apartment (eg. the save point, the chest, the bed), but I think the most annoying had to be the victim crawling out of the wall, which would hurt you NO MATTER WHAT ROOM YOU WERE IN. I mean, the laundry room is really tiny and just serves as a portal to where there are more life damaging enemies anyway, you're practically losing health for no reason, which is a gyp.
All the rest were pretty tame because they didn't really get in the way of anything important and you could (in most cases) just dodge around them if need be.
I never saw the Walter painting, Henry at the door, or the cat in the fridge. I probably would have been unnerved a little at the cat one, since my cat scares the hell out of me at nighttime on a nightly basis.
