Streak's extension for Gmail is installed at a browser level. This means that Streak is available in all accounts you've logged into with that browser.
If you do not want to use Streak in a specific Gmail account, though, you deny Streak's access to it by clicking the Don't show this again link at the bottom of the window we open for log-in.
Remove from a specific inbox
If you've already logged into Streak and provided it access, you can revoke it from a specific account by following these steps:
Log in with the account you'd like to remove Streak from
Navigate to the Permissions page of that account
Find Streak in the list of Third-party apps with account access and click the entry
Select Remove Access
Refresh your Gmail
Using Chrome Profiles
We're huge advocates for using Chrome's Profiles functionality, too, if you're looking to enforce more separation between your business and personal browsing experiences.
This allows you to keep Streak sandboxed to one profile, while keeping it out of your other profile.