Ok, so with 20 votes so far there seems to be a tie between the dining room and the half bath. I guess that bathroom wallpaper is far more offensive than I thought. Some small disillusioned part of me was reminded of something by Josef Frank (see links) only gone terribly 80's wrong.
I'll wait for more votes but the good news is those rooms would be the easiest and fastest to take down. Famous last words right? The crisp peeling edges of each strip of paper are just calling to be pulled down, even it knows its days are numbered.