If you're not content with broadcasting your latest blog-post, obsession, or 140-character sluice of brain-diarrhea to your Twitter followers, V2_ Lab's Pocket Tweets can help you take those messages into the real-world. Their Java app displays your latest tweet on your cellphone; cut a speech-bubble into your pocket and you can happily parade around inviting people to read your chest.
Pocket Tweets was created as part of an art exhibit for the Wearable Technology AIR project in spring 2009, but that hasn't stopped them releasing the Java app at the heart of it. You can download the software and find instructions of how to use it here.
Of course, you'll also need to cut out a suitable hole and do some stitching to make the speech-bubble, so if you're inept with a needle and thread then it might be an idea to ask your mom for some help. It doesn't have to be a shirt pocket, mind; you could also have your rucksack displaying your latest tweet, or even your briefcase if you don't mind taking a small hacksaw to it.