Doing the Full Stack Nanodegree from Udacity
Using Google's oAuth Sign in in my Flask App, I realized that no matter what browser I use, I was unable to logout, Google always threw an error my way. I figured something must be wrong with my code..
Searched on Google, couldn't find anything relevant, gave up on first 4 results(not pages, yeah I'm that lazy!)
Spent 3 hours Debugging at different points, removing all the abstraction I've put in using various libraries (Bad move)
Finally it dawned on to me to check Udacity forum as well. It's a frickin cache/cookie thing. Tried the app in an incognito window, worked like a charm. Reverted code back with all the libraries, worked like a charm again!

FUCK YOU GOOGLE! In your attempts to track users, you're even making our work difficult!

(in hindsight, I should probably be better at asking/looking for help)