I'm telling y'all, it's sabotage
Sometime between stashing Avenger Much-Abused Hybrid in the bike room on Friday evening and bringing it back up on Saturday night, the front tire went flat. Not sort of flat, getting to be flat, or almost flat, but flat. Completely flat.
Owning multiple bikes, I was in no hurry to spend an evening prying a filthy tire off the grimiest of them and checking it thoroughly for some malfunction. But I finally just did so, and thus confirmed my suspicion: There's absolutely nothing wrong with either the tire or the tube.
Conclusion: Somebody deliberately deflated it.
(If it's who I think it was and for the reason I think it's for, they'd probably bitch at me for being so ungrateful to them for not stealing the damn thing.)
So, no more bike room for my bikes. I liked to stash Avenger down there (as I'm supposed to all the time anyway, according to the building rules) as a courtesy to my neighbors during peak elevator-use periods and/or when he's dripping wet, but if my neighbors are going to be assholes about it, then they'll just have to deal with the fact that I keep my bikes in my apartment and use the elevators (did I mention that I live on the 13th floor?) to transport them.