What's caused you to drop a neighbor?

I delete people after that don't play for a few months, don't have roads, dump everything, have designs I don't like, or whatever, but accept new people on the reg. It's nice to see how people use different items.
There is no social game so I'm not attached and don't necessarily need neighbors. There ~are~ a handful of people I still have as friends for nostalgic purposes. They haven't played in forever but I can't bring myself to delete them.