Here's a prank perpetrated on the Skype system (an internet-based phone and chat service) that proves you never know who you're talking to online:

A profile is put up with a girl's name and picture, and put in "Skype me" mode. Within minutes some seedy guy will invariably try calling/chatting, and there's a little program I made running the whole time which will partner up people 2 at a time, and send messages from the first person to the second, & vice versa. This way both people think they're talking to a girl, when they find out, well, they're not normally too happy about it...

It reminds me of the VixenLove program (which was a computer program designed to simulate a 19-year-old girl). But this is better, because it pairs up two real people and makes them waste their time hitting on each other.