Second this.
I started slacklining about a year ago and before that I was the least 'showboaty' guy ever. But you need trees to slackline, over dry grass preferably, so parks and greens tend to be the best places around and that means there is a lot of people around. So I just had to get used to the fact people would watch especially as its a new sport and not too many people have witnessed it before. Didn't take long before I got used to them and it's even got to the point where I like it... It spurs me on to take bigger jumps etc.
Its the same with trials, I mean I've only just started so I'm shit and I must look like a dick to people passing learning to trackstand and whatnot...
So to begin with m8 you just gotta say 'f**k it!'