Press F12(default) to activate the pitchup, then move your mouse up and up untill it wont go anymore.
Play from here, you can move around now.
If you want to look normal just look down again as far as it will go.
Made by Sin, tfcscripts@hotmail.com

Advantages for this script

It makes your body look smaller to other people

to start it working you could add a line to the autoexec.cfg as "exec bodyflip.cfg" (without quotes) or type it in the console in game.