It should be a simple thing: deleting email addresses and info for contacts you no longer want to see autopopulate in your Gmail account. While Google never added a contact listing for that cloaked Craigslist email address messaged once about concert tickets, the info still exists in your contacts, ready for you to accidentally mark as a message recipient. Time to clean the little black book part of your Google account.
There are a few ways to access a Google account's contacts. First, when signed into Gmail, click on the drop-down menu labeled Gmail in the upper left corner, under the Google logo. Select Contacts, which will then appear grouped into categories like Starred, Favorites, and within Google+ circles. The category Other Contacts is where all those random addresses will appear. Select any you'd like to delete, then click the More drop-down menu and press Delete Contact. Et voilà .
Alternatively, access contacts outside of Gmail with Google's Contact Manager. That'll take you straight to the same list of contacts found using the above Gmail steps.
If you have a change of heart about any of those deleted contacts, Google will let you recover them for 30 days, but after that deadline, they're gone for good.