Noting for the crowd that Google user accounts also have a checkbox option under Connected Accounts: "Use my Google contact information to suggest accounts from other sites."

I have no external connected accounts, and I have now unchecked this option just to be sure Google stalks me less. Not that I'm sure it'll be meaningful due to all the link-jacking Google does in its own products, but at least they won't be trying to plug all my personal accounts into their database at the same time.

All this so they can simplify their identity database for the sake of advertising. Sigh.