Oh gosh, I swear I could have written this post - I am totally with you on feeling like there are some places that would look down on the likes of very boring and below the cut little old me. I would probably end up trying to make myself as small and inconspicuous as possible in a place that is purporting to be so la-di-daa. I'm a bit of a cow like that though, I don't like establishments that look down on people based on their assumption of your class.
And one sugar cube? If I was going to pay £4 for a coffee, I would definitely expect more than one sugar cub and at least a little biscuit.