iOS: The free iOS app Sarcastic Samantha does one thing and does it well: Enter any text, and Samantha reads it back to you in a Siri-style voice, adding a sarcastic comment such as "I'm so blown away right now."
The advertised use is to tell whether your ideas are good enough to survive this withering delivery. But I find it great for pasting popular tweets that I hate, filtering them through this little voodoo doll instead of bugging my friends on chat. It's my own private dislike button.
Samantha has three friends, each with their own voices and their own withering remarks. My favourite is the slightly Jobsian Condescending Carl.
Sarcastic Samantha [iOS App Store]