When you park somewhere and have to pay by phone or an app
Yeah fine if you have the app set up. But it's always a different one to the one you use. So you have to download it (inevitably it's in an area with crap signal) sign up, confirm your email, put your card details in.
Then you look properly at costs on display and realise it's Sunday and it's free and you've just paid for a weekend
see also takeaway delivery apps.