Caught by my flat mate
I've been caught a few times but one very positive experience was when I was a student and spending a year in Spain. I shared a flat with another couple of British student who I hadn't met until I arrived in Spain but we all got on very well. At I was 20 at the time and although I always liked to spend time nude I hadn't really considered myself as a naturist of even given much though to the whole naturist culture.
One Saturday my flatmates had gone out for the day so I found myself in the flat by myself. I got up and showered without giving things too much thought decided to make the most of the opporunity to spend some time nude so after drying myself just left my towel in the bathroom and went about my morning - some breakfast, a bit of clothes washing etc and a bit of studying at a table in the sitting room. The sitting room was at the far end of the flat with a corridor from the entrance that the other rooms opened onto.
Anyway, after a couple of hours at home alone I was startled by the front door opening and the voices of my flat mates returning home. I was nude in the sitting room with no where to hide and quickly looked for some clothing or something to cover myself up. I couldn't find anything and went into a bit of a panic so hid behind an armchair (unsuccessfully) racking my mind for a goood reason to be naked.
They walked straight into the living room and saw me trying to hide immediately and asked what on eart I was doing. Then they spotted I was naked and thier immediate reaction was 'Oh my god you're naked!'
I was so embarrassed but had to come out from my hiding place and they just stood there looking at me in shock. I ran past them to my room apologising, grabbed some shorts and then came back out to face them and try to explain. The first thing I came out with was that I was a nudist - which of course was the truth but I hadn't really considered it or told anyone before.
That changed the tone entirely and they were completely okay with the whole situation. And the best thing is that secret was out of the bag so I was able to be clothes free far more often and they were very comfortable with me being naked around the flat with them. By the end of the year everyone pretty much expected me to be naked in the flat.