If like myself earlier, you try sending a picture along with a tweet using the official Twitter app for Android and it sometimes doesn't send, but also doesn't give you a "Failed to send Tweet" error, you'll be familiar with "Sending Tweet..." being stuck on your dropdown thing.
Sadly, it doesn't disappear when you stop Twitter's process (in the "Running Services" option in your Settings) and you can't swipe it away (well, depends if your version of Android allows you or not) and this is a problem I have noticed all around the internet on various places. So how do you fix it? Well you could just reboot your phone... but in this day and age of fast communication, rebooting is time consuming (I know less than a minute, but heck, that's a lot of time!).
So here we go, a quick and very simple way of removing it...
1) Go into your "Settings", scroll down and select "Applications". When in "Applications", select "Manage applications".
2) Find "Twitter" and press it.
3) When on that page, just tap the "Force stop" button and select "OK" on the popup.
It's gone and without the need to reboot your phone. Now fire Twitter back up and you should still be all logged in and ready to continue.
Told you it was quick and easy. :)