OP, YANBU. Nowt wrong with being middle class. Definitely something wrong with being insufferably smug about your class status within your own self-defined hierarchy though. Tbh, of all the people I know, the ones who are most guilty of this are my friends from the North-West who take massive - and vocal - pride in being working class. They are - among other things - lecturers, doctors and accountants. One of them is a decorator, so I'd consider letting him off, except that he is a decorator who specialises in the treatment, removal and application of antique wall-coverings.
Anyway, I also have friends in the landed upper classes and they're the easiest when it comes to this thorny issue because they have no idea about what the class system is, how long its existed and why it's discussion might have the potential to cause offence. Frankly, they are too preoccupied with wondering why their James Grieve orchard had such a bad crop in the Autumn.
Generally, you can ascertain someone's class by working out who they hate:
Working class: hate everybody except builders.
Middle class: Will hate other middle class people for being so middle class. Won't admit to hating anyone else but will avoid sitting next to anyone reading The Star on the tube/bus.
Upper class: "Golly, don't think my family has hated anyone since the Hun. Though to be honest, I think Himmler may have been a distant blood relative."