Oh man I know EXACTLY what you mean and I hate it. Some people just think flips are for showing off and can't comprehend that we might actually be doing them because we think they're fun, or we want to practice them. School just happens to be a great place to train.
At one point I got sick of trying to find places without anyone around and now I just don't care what they think.
Plus showing people stuff isn't the same as "showing off", like an artist displaying their work for others to see, we should be able to express our dedication to our discipline whenever we want without people judging us, but hey it's usually the jealous type who says that anyway.
I admit I've done stuff in front of people sometimes, I still laugh when I think of the time I was working 3 step wallflips on a grippy wall and this kid came around the corner with his friend and he was like: "Holy sh** dude, that kid!" haha