Without a doubt, when dds were very small, a hotel in a Portuguese resort near the Spanish border. We went because a BiL and SiL with their dcs and extended family were there.
Arrived to a very glum face on BiL. Water was off a lot of the time and nearly all of their party were ill. Not long afterwards I found dd1 (then 4) trying to brush her hair with the loo brush in our room! ?
Thankfully we didn’t become ill, but I found the staff so unhelpful and surly. Dd2 was only about 15 months and still wanted a bottle a couple of times a day - trying to get them to bring me boiled water, or anything like a plain boiled egg or toast for dds, was a major battle every time.,
After 4 or 5 days, with the water situation not much better, I’d had enough, and dh went to the tourist office to ask for a better hotel. (We weren’t on a package holiday.)
There was a large, locked cupboard thing in our room, which, having never seen such a thing before, I’d assumed contained linen or cleaning things for the staff.
However, shortly before we actually left, I saw one open in another room that was being cleaned - a mini kitchenette!! I was flabbergasted - went straightaway and asked reception why, when I’d been battling to get boiled water and toast etc., for dds, nobody had told me that there was a mini kitchen in the room.
Surly, unhelpful cow on the desk just said, ‘You didn’t ask.’ Well, that was because I’d never known such a thing before.
We moved to a nicer (more expensive) hotel, with considerably nicer staff, but the sea was rough and bloody freezing.
I dare say it’s unfair of me, but I was put right off Portugal and 40 years later we’ve never been back. Or rather I haven’t -dh and a dd did visit a nephew who’s doing a PhD in Lisbon recently. (Pre COVID of course.)