Tell him he is legally responsible for all the traffic that goes through his router. That'll make him password protect it.

Should come up with router name "FBI Surveillance Van" that oughta work.

set the password yourself

Set up your computer with the same name as the one your wifi has now. Hide your current open wifi. Now all traffic will go through your computer and you can, if you read it up, gather sensitive information from everyone using your new open network. Now do as you please! (f.eks enter their Facebook, email, YouTube, etc. Send a message directly to their computer, or simply just block them out.)

****. But nice try, OP.

Why don't you put the password yourself?

why don't YOU password protect it...?

Idiot.

I would start sniffing the network and steal passwords from all those who use it :)

Password protect it yourself, dumbass :/