Every time when you receive a piece of code and it doesn't work.

But then you ask them to show you and it never actually worked

@jimmyscene Usually it "mysteriously" stops working for them when they want to show it.

Been there. We had some dates and times showing on a website and it works correctly on my and the front-end devs machine (windows and Mac) but doesn't on the PMs and customers (12 hours clock used whereas we see 24h clock format)