How can I prevent a different account from trying to sync my iPod?

When I plug my iPod into my iMac, it suddenly starts saying it is syncing, and to not disconnect. Of course, I disconnect immediately because I don't want it to sync! In fact iTunes isn't even open and doesn't try to open. If I try to open it, I note that I haven't even accepted the iTunes license yet! So why is my iPod trying to sync with another user's account?

Just to be clear, this iPod has been synced in the past using a different login account, before the iPod was given to me. But I don't want it to do that anymore. At the same time, I can't just disable syncing on the other account, because the other user doesn't want it disabled for their own devices.

What is worse, when I do accept the iTunes license and then go to iTunes:Preferences:Devices I see that auto-syncing is disabled. But with iTunes now open, when I plug my device in, it still tries to sync!

So I try to temporarily disable auto-syncing on the second user account (strangely, their iTunes isn't open either, even though the iPod says it is syncing). But it still says syncing as soon as I plug it in. How can I stop this?! And what is it syncing with since neither version of iTunes appears to be running?