We've all had them, and as dissers we would obviously rather post about them than deal with it, so now's your time!
Mine reached peak P-A yesterday when all 4 of us were in the living room watching Wimbledon final only for one of the other couple to casually ask the other "is there many people down there yet?" referring to the downstairs flat, to which they 20 minutes later without a word to go to a party in the downstairs flat LOUDLY. I wouldn't mind so much but like we've also met and hung out with the downstairs people a couple times and got on so it's not exactly like (it seems anyway) we'd be out of place or not welcome.
Anyway a couple hours later one of them comes back to show someone from the party his guitar set-up, proceeds to play that real loud for a bit (so both upstairs and downstairs noise now) and then leave again without a word.
I can only assume we are in fact terrible people, but this still seemed like bad form. At least it rained on their stupid BBQ...