**I love being a bibliophile.
I've learned that one of the better things to imply disinterest towards anyone is to take out a book and start reading while they're looking. In the event that you don't feel like listening to their brainshit yapping no more, then wait for them to finish what nonsense they're talking about. You can maybe force a nod to fake agreement, hell, force two nods for good measure, and then go back to your bookmarks. Timing counts; it makes you less rude than you have practiced to be.
A bigger book guarantees your point goes across, and I make sure I have one when I'm feeling like its going to be a decidedly long day. A paperback works too; it's like your swiss army knife, your panic button, because its size makes it available to you anywhere you go. There is safety in convenience because there's no telling when you're likely to encounter more than your daily share of really boring people. Magazines offer very little resistance because they don't last long. The bore will probably get it the third time you're reading from page one. That kind of defeats the point because I'm after the discretion here, and they aren't supposed to notice the conscious effort.
Of course, make sure you're reading something interesting. You're going to be more occupied that way, and that takes care of the body language you need to accentuate your disinterest.