irritated by interrupting coworker

A reader writes:

Here's something kind of petty, but it's getting to me. Every time I ask my supervisor a question, one of my colleagues (who sits next to my supervisor) butts in and starts answering the question too. Suddenly what could be a quiet, 2-minute discussion is turned into a loud conversation. Grrrr. Every time he does this it throws me off track.

Why do people find the need to interfere in this way? Don't they have enough work to do? Do they really have to prove to the world how knowledgeable they are every second of the day?

Ah, I'm probably being hypersensitive because this guy is not great at his job -- lazy and disorganized -- but is a champion schmoozer, very self-satisfied. So you'll probably tell me to just grow up, and rightly so, but I'm hoping someone will have some insight so I can control my irritation better.

No way, I'm not going to tell you to grow up over this. It drives me crazy too. I think there's only one way to make it stop, and that's to address it head-on. The next time it happens, say something like, "Actually, I really wanted to get Jill's input on this. Would you give us a minute?" If he doesn't back off, say it again: "Thanks. Actually, I really want to talk to Jill about it." Say it nicely but be firm about it.

As for your question about why he does it ... Insecurity might be at work. You mentioned that he's not that great at his job, and if he realizes that at some level, pushing his opinions on all who will listen probably pumps him up in his own head. Doesn't mean you have to accommodate him though.