So instead of just getting something that looks good and non intimidating on certain occasions why not get a Victorinox classic or my choice the Mini Champ. You put these on your keychain and now you have a great utility knife with additional tools (especially the minichamp) that will always be handy and carry your tough guy knife with you also and then just leave it behind when you feel it's presence is inappropriate. Nothing is less intimidating than a SAK since it isn't single purpose.
Just my 2 cents. As far as non intimidating knife, any SAK works, lets face it if you had to pull one out to defend yourself you'd liably could be defending your self with a can opener. Which is why if I feel a need to carry a knife for self defense, I'll get a gun instead.