So I work in retail in London, UK. I'm at the tills in a store that sells everything related to fashion (men's, children's, women's, lingerie, swimwear and shoes). I get to see the stuff people buy. And I've had a good number of customers happily buy several bikini sets and pairs of sandals because they are going to Spain. Like, next week.
I'm starting a thread today because yesterday my colleague was serving this lovely lady and suddenly she says 'oh, Irene is from Barcelona! The lady is going there tomorrow :)'. So I'm like, 'great, it's going to be a bit milder than here'. And she goes, 'what do you mean?'. 'Well, it's still winter, but it's milder, so you could probably get away with wearing a parka because you are used to the colder weather...'. I mean, we've had SNOW in March in the past. It's uncommon, but it gives you an idea of how 'hot' it is. She stared at me in disbelief. The lady had been packing for a summer holiday. In March. Spain is not a tropical country. She cancelled all of her purchases and said she was going to cancel the flight, too, because it was her anniversary and she had been expecting the weather to be really hot and sunny. A quick conversation with my mother at night reassured me that it's actually going to rain this weekend.
I feel sort of guilty about ruining this lady's dream of a summery vacation mid-March, but it's not my fault if she didn't bother to check the weather forecast one day before her trip.
I also had this lady whose husband was taking her on a surprise trip 'to Spain'. She was also packing bikinis. I really hope he was taking her to Canary Islands, because if she was going to the north...
I find it slightly amusing that they truly believe that it's always sunny and hot everywhere in Spain (or Italy, or Greece, or Portugal), when there are actually places in these countries that are far colder than England (especially London, which is not even that cold... jeez). Then we see them in March walking around Barcelona, short skirts, sandals, their legs covered in bumpy skin and a blueish tone due to the cold.

British ladies, please do not do this to yourselves! Go to Spain, or wherever you want, and enjoy your time there, but wear appropriate clothes, and always check the weather forecast before visiting a place

PS:
'But will I use the sunglasses?'
'Well, if it's sunny...' -I shrugged. Actually, no, you would not have this particular weekend

'And what about Málaga?'
'Well, I don't know, that's southern Spain (Barcelona is IN THE NORTH) so it might be warmer there...?' -just checked, it's not any warmer there right now