Ahaha xD
Well... If I was you (don't trust me, I'm just a 6hkyu begginer), I would tell him that that conclusion was up to him!
Aikido works! I've seen (and felt ahah) that it really doesn't take strenght, it takes energy!
Don't hurt him, that might lead to two opposite reactions:
1- Woooww it really works! Teach me, master! ahah
2- I'm getting outta here!
Let him find out by himself!
Peace!