Don't beat yourself up about it, they shouldn't have been doing it. If you feel bad about it though it's because you know it wasn't the way to resolve your problem with them.
In an ideal world, if you have a problem with the way they treat communal areas, you talk to them or write a note...
If you did it because you think they shouldn't claim benefit and work, fair enough. But if you did it out of spite for them parking in your preferred parking space or something, you are a bit of a petty gutless wanker.