Really, the very fact that you're concerned means that it exists and is something that needs to be considered. You're the best judge of what obstacles you encounter, and if you think you have a problem then you do.

Everyone that comes to Parkour from our kind of society experiences that effect to some extent because we're all conditioned to avoid embarrassment wherever possible.
The longer you spend practicing Parkour the more confidence you develop in those kind of situations. When you understand what it is you are doing and feel comfortable in your choice of activity, when you have developed a strong opinion of what you do yourself, then the opinions of others bother you less. Just keep practicing, keep thinking about what you do, keep trying to get better at explaining it, and your confidence will improve.