I've been to a few Hermes stores around the world and I've never encountered any rudeness - I'd think anyone working at Hermes would both value their job too much and feel the weight of their behaviour reflecting on Hermes' reputation on the whole to be rude... but I always have a feeling I am being appraised when I enter. So whenever I go I am conscious about dressing well. I haven't tried walking into an H wearing flip-flops and pyjama pants, so I don't know how that would work out - maybe I should try!
I think that being afraid of walking into H in pyjama pants is in itself a sign of underlying social issues that need fixing. I understand the argument that H is a high fashion establishment and deserves respect by making an effort to be presentable, but on the other hand I think it's fashion for people and not the other way round - if you feel bad, the weather is awful, or you just really don't want to dress up going shopping - you should, in a free world, be confident not to be judged for being human. Unfortunately, I've heard many stories of people being ignored in luxury stores or even asked to leave if they were not dressed in accordance with the SAs' expectations of standards.
I very much like luxury shopping - the experience, the quality..but it is all the same very sad that a lot of these brands seem like fortressed clubs that don't want or even need any new members - they are happy to serve their vip clientele and the priviledged few and may well be cold to those outside this circle. SAs, though human just like you and me, may be subconsciously channelling this mentality, unwittingly appraising, perhaps surprising themselves at time.
This, of course, is a very cynical view of the fashion world - I tend to be cynical about a lot of things. Reality may well be brighter...I'm staying open minded.
This aside, while I have not personally encountered rudness, I'll note that Hermes SAs in the Prague store are incredibly curt. Honestly I didn't hope to get much out of it because it is probably one of the tiniest H I'd ever seen, with enough room only for a gargantuan Bolide, an Evelyne or two cowering below it and a croc briefcase that was recently bought by a very handsome man in a pink suit while I was there shopping. But I noticed that no matter how many times I'd come there, buying a trinket or scarf, the SA is always curt and very cold. Relationship building failed, it seems!

Good luck everyone