This is a really good question.
I often use the line; "I love work, I could watch it all day long"
I usually start with asking if they are waiting for the machine, and let them know about how long it will be before I am done, and then I also always make sure I blow the machine clean with compressed air, before I work on it, making sure anyone around knows they may not want to be there as I blow the dirt off.
I also try to act as if I want to teach them everything there is to know about their forklift, (it works in a 'reverse psychology' way, I -want- to tell them, so then they don't want to know, and they seem to have more important places to be), and I am willing to go into all sorts of useless {to a forklift operator} details about any forklift component, all the way to remembering going fishing, to a hockey game, or rodeo with someone that works manufacturing forks, chain or racks.
I am in a part of the world that has very few unions, so I also tell people that I am not really in any union, but 'my union rules' say that if they have to watch or sing near by, then they have to listen to my bad jokes, and I promise them my bad jokes are worse than their bad singing. I also tell them the 'union rules' say they have to apologize if they are going to interrupt me in any way, they are welcome to interrupt me, but they have to apologize first, just an "i'm sorry, but I don't care about interrupting you, etc..." is fine, as long as it starts with an apology.

I have had some jobs, in other countries than the USA, where the work permit law made them have a "sponsor" to be able to hire someone from out of their country, who had to be paid the same as I was charging per hour, and who had to stay with me while I worked. they were always glad ($) to have me around, and never made themselves a problem.