People are using a report of one small incident to decide that Justin Timberlake is a jerk. How sad.
There's a lot we don't know, like was the guy videotaping really just a dad taping for his teenage daughters, like the OP thought? Was this the first encounter, or had he been taping in another part of the park before the OP saw him and this was the second or more time he was asked to stop? Had someone who looked like the guy gotten in Timberlake's face and this guy was the (unknowing) recipient of anger that was aimed at someone else? Had other people been hasseling them and this guy was just the strw that broke the camel's back? We don't know.
Keep in mind that Justin is a 23 year old guy (one with millions of dollars who has been a celebrity for quite a few years, but he's still only 23). Do all non-celebrity 23 year olds treat everyone politely every minute of the day? I don't think so.
I'm also not excusing rude behavior; just saying that we know very little about this incident. So, although his behavior as reported appears to be rude (although we don't know why he was as rude as reported), I certainly would not conclude from the report that he is a jerk, deserves his 15 minutes of fame to be finished, is trying to "game" being a celebrity, etc, etc.
I don't know what it's like to be a celebrity, but it can't be as easy as it looks from the outside. I do know that Minneapolis used to get a lot of recording industry celebrities coming to town when Jimmy Jam was producing here (he moved to LA). A lot of them tried to go shopping at the Mall of American, but even with disguises (mostly hats and sunglasses), they were found out. A lot of times fans who recognized them called friends (or radio stations) with their cell phones and suddenly a little shopping trip turned into a small riot.