When I'm taking pictures I'm very focused and I really don't want to talk about what some guy did with his camera club last month.
People with expensive cars like to take pictures of them, so I get sucked into gear talk all the time in the field. I try to be as polite as possible and answer their questions, but when I'm on deadline and the clock is ticking, it's definitely a distraction.
What never ceases to amaze me is how many people feel entitled to give you photo tips and advice while you're working. I had one dude recently offer unsolicited lighting advice while I was lighting up his buddy's car. Mind you, earlier in the day he showed me a bunch of snapshots he took with his 5D2, Alien Bees, and some expensive primes that could have been taken with an iPhone. At this point he had no credibility, but then he went on to complain about how much the 5D2 sucks in low light, which only compounded matters. Fortunately he didn't take offense to me ignoring his "advice," but believe it or not, a lot of people do.
Don't get me wrong. I love talking about photography techniques, and to a lesser degree gear, with photographers who have useful information to share. That said, I would never tell a working professional in any field how to do their job, especially while they're working, and then get mad if they ignored my useless advice.