My friend a backend dev who manages a little UI by using bootstrap themes. One Saturday he calls me up says "Dude, I need your help, we had a demo and the CEO decides to demo the project to prospective people on Internet Explorer. It looked alright on Chrome but the whole UI has gone haywire on IE. Need your help asap. Join me on screen share". I checkout his HTML code and find a file where the link tag is inside the body tag. I ask him to move that into head tag as in wherever the master template is, I tell him to change the doctype, add responsive meta tags, and even after all these, it just doesn't render bootstraps media queries. After beating my head for around 15mins, I see a drop-down caret in IE's inspector with 7 besides it, someone had set the compatibility mode to IE7. Why in the world would someone set an IE11 to IE7.
My friend heaved a sigh of relief and walked to his boss to show that he isn't a bad developer, his boss is just a bad user.