Thank you for your report! Your ID is correct, this is bittersweet nightshade. It is a common weed and is not regulated, but it is one that you can pretty easily control. If you're able to chat with your neighbor, digging out and disposing of plants is effective. Or, you can try an herbicide like Roundup, the one labeled for woody plants may be needed - just be sure you follow the label's instructions and do not spray non-target plants.
Best,
Lindsey

Lindsey Wise
Sept. 19, 2019, 4:27 a.m.

For a lot more information about this plant, see https://your.kingcounty.gov/dnrp/library/water-and-land/weeds/BMPs/bittersweet-nightshade-control.pdf

Lindsey Wise
Sept. 19, 2019, 4:28 a.m.