Left 4 Dead Pill Glitch
Quick video of the pill glitch in the PC version of Left 4 Dead.
Higher quality version here:
http://www.xfire.com/video/65432/
I've already reported this to the Valve L4D forums, so don't bother. Seeing as how this glitch doesn't really affect anyone negatively, I'll tell you how to do it. The person with pills gives the pills to another Survivor, who should be spamming the melee button (right click). As the person who is giving the pills right clicks to throw them, continue hitting the melee button and look at the other Survivor, and the pills should keep flying in between you two as long as you're both meleeing.
*Sorry for the lack of audio and shitty quality, its recorded using the Xfire record function