[jawfin]

This script will allow you to assign a key that once pressed will leave your player crouched without you needing to hold it down. This specifically makes crouched fanning more easy.

//Toggle Crouch by Jawfin

//This key is for normal crouch - and will negate the toggle crouch
//It also has to be set in the cvars _cr1 and _cr2
// so look below for them
bind KP_ENTER "+movedown"

//This key is for normal jump - it negates the crouch
bind KP_PLUS "+moveup; -movedown; set _CR vstr _cr1; bind KP_ENTER +movedown"

//This key is the toggle crouch
bind KP_DEL "vstr _cr1"

//The actual toggle crouch code - fix normal crouch binds here
seta _cr1 "+movedown; set _CR vstr _cr2; bind KP_ENTER vstr _cr2"
seta _cr2 "-movedown; set _CR vstr _cr1; bind KP_ENTER +movedown"
set _CR vstr _cr1

//Always remember to leave the last line blank in a script

Note that pressing the key again while you are crouched will not result in you standing up. This way you can hammer the key without worrying about what state it is in; useful if you are jumping in.
If you want a challenge, try to rewrite the script so it can stand you up, but it is a lot more complex.