Recently learned about this glitch after reading about it on the forums. Makes for some pretty funny screenshots hehe:

http://imgur.com/smKAZpF

A video of the glitch in action (not by me):

www.youtube.com/embed/6ipJau9Vw2g

Unfortunately it looks like its only visible on your screen. Others cant see it :(
here's how to do it:

1. /sit on a chair or bench
2. make a macro for an emote
3. hit the emote macro and the move forward button at the same time

You'll know you got it right if your char walks forward while doing the emote animation. And when its finished your upper body should lock into place. Works on mounts too:

http://i.imgur.com/F7Ecmp9.jpg