Been there before myself, and communal laundry facilities in an apartment complex can be a real pain in the ass. What kills me is when a WHOLE FUCKIN DAY passes and you are checking on their shit every 3 or 4 hours and it still hasn't been moved. Depending on my work schedule I would finally just lay their clothes on a table or wherever.
The worst was when I had the complete opposite happen to me. I went to take clothes out of the washer , and found my stuff in the sink with the washer running with someone else's shit. They obviously interrupted the cycle because my clothes were soaking drenched and never went through the spin phase. So I put my laundry in the dryer and then took their stuff out and threw it all over the floor, the nastiest corners I could find, everywhere.
I went apeshit and started yelling for all could here..."whoever the fuckin dickhead was that messed with my laundry, can now find it on the floor. Although, I'll be here for at least an hour guarding my drying cycle, so unless you want to deal with me, I suggest you come back later".....along with a litany of expletives. This is one of the many cases where being known as the crazy assertive guy can be a positive.
I grabbed a book from my apartment and camped out till my clothes were done, and only a couple of neighbors came up after hearing the ruckus getting a good chuckle since they didn't do it and was hoping to watch me throw down with someone.
Only advice I can give is try to do your laundry during weird hours when most people are at work or asleep...lessening the probability of having to mingle with lazy and idiotic people.