Bizarre habits

I have a flat mate who picks stuff up on the street he thinks might be useful, regardless of whether we need it or not.Recently we acquired a cd rack that has just been in a corner doing nothing and once there was a mains water works pipe connector thing, that I have no idea where he got it from or why he thought picking it up would be a good idea.My favourite one was the bike that appeared...So there's some little bike rat/kids that always leave unlocked bikes in the stair well of our block. The bikes are always changing and being sprayed different colours and often have different wheel sets changed between the bikes. (The police have been round several times but nothing is ever done) I came home after a night out once to find this gold spray painted mb in the living room. My first thought was st someone’s broken in taken our bikes and left this, I took a look round and nothing was missing and no one seemed to be about so I left it there in case someone’s friend had left it there for a reason. My flat mate appeared after several hours and when I asked him about it said "I didn't think anyone wanted it so I brought it up." He then left the flat with the bike still there. I was weary of taking it out in broad daylight so I thought I'd take it out when it got a bit later. Then on my way to the shops I heard a fairly large group of rude boys on the stairs accusing each other of the theft of the said bike. I waited till I was on my way to work the next morning to drop it back in the staircase and on my return form work saw the same group of boys having a massive debate about who was trying to fk with them, it was at this point I decided that my flat mates weird streak was actually quite funny as no harm had been done and the kids who I assume are committing a large amount of bike related crime felt what it was like to have something of there’s go missing…I’ve just realised that was totally off topic pretty much, but works sucks.