Jaxson: Hotel/airline booking sites that still default the checkout/return dates to today.
Eg I book for March in 2018 and then the checkout date still defaults to today, meaning clicking another 12 months ahead to get near the checkin date...
Actually calendars that start the week on Sunday on some, and then Monday on others (Air NZ). I think I prefer the Monday start, as it groups the weekend days together.
Ticket sites that lock you out saying stop the bots, but don't give any indication as to what's causing it.
Likely lots at work trying for the same tickets, on similar IP address; or in my case, having two browser windows open at the same time.
Then presenting robot check picture panel tests that even it gets wrong.
And ticket sites that offer seating options (lounge/open air??) that aren't shown on the basic event seating chart/plan, so you have no idea where that is.
Actually most seating plans for most events really.
Oh and ticket sites that sell by areas, then list specific seating numbers, but offer you no info as to where those seats specifically are within the giant pink blob that is covered seating etc.
I think your complaint is about programming stupidities in general. Lots of those.