The next time you try kote gaeshi on your friend, don't say anything, just grab him off-hand and throw with kote gaeshi, and see what happens.
If you pay close attention to what was different and the possibilites as to why it was different, I think you will pick up on some "secrets" that will guide you in your training.
Just out of curiosity, how long have you been training?
uhmm... I think I would refrain from forcing anybody who are not trained in ukemi to take a kotegashi fall. Especially if it's outside of the dojo. Quite a big risk of hurting them badly.
Apart from that I think Michael is right. The 'tensing up' that will follow from the expectation that something is about to happen that may include pain will ruin any aikido technique. The thing is - as I see it - aikido dosen't really work unless uke is comitted to the attack, and that situation is just impossible to reproduce outside of the dojo unless it is an actual fight. Disclaimer: I am NOT encouraging you to pick a fight with your friends ind order to demonstrate Aikido
Point is - it takes a long time of practicing with reduced power and speed and a lot of cooperation before aikido becomes fluent and effective. We learn to react to the locks and that is what makes it safe for us to practice on the mat at high pace. If applied full speed on an attacker that is comitted to attacking you will most likely result in serious damage to him (or you if you don't get out of the way).
I rarely demonstrate anything on non-aikido people anymore except from nikkyo and yonkyo. It is not techniques that by them selves really show the essence of Aikido, but they can be applied with moderation and proves some aspects of the effectiveness of aikido.
My advice: get your friend to come to the dojo for a few months and try it out.
Have a great day