For me my biggest embarrassment was my first night out at university. We turned up to the club and every other girl was wearing skirts/skinny jeans and short-sleeved tops, and I was out in my casual jeans, a dark t-shirt and a suit jacket/blazer over the top.
It was my favourite style at the time, and I realised I was wearing different to everyone else whilst we were out, but just didn't realise how out of place I looked until I saw myself in photographs. On evenings out I still don't dress like others, but I now aim for black trousers and a slightly 'fancy' short-sleeved top. It makes me stand out a little less, and as I grow older there are fortunately more and more women covering themselves up a bit so that I blend in with them.
Day-to-day, I now own one style of jeans and one style of shorts, and the same t-shirt every day, so that's something that I don't have to think about. Very casual, but I'm comfortable with how I look in that outfit - I prefer casual comfort over fashion.