This post gives a few ideas: https://webmasters.stackexchange.com/questions/15552/how-do-you-exclude-yourself-from-google-analytics-on-your-website-using-cookies
A variation on what they have..
Where they suggest custom cookie values, you could create a page on the website that sets that value e.g. www.mysite.com/opt-out, bookmark and always use that link first and all visits from that user can easily be excluded. It does rely on starting on that particular page though.