Howdy ho there. I've been using basic command prompt at my school for about a year now and I recently joined a friends network, via hamachi.
I've been wanting to play a few tricks on him and I tried to taskkill him. Just for a few laughs, nothing big you see. So first, I did the

"tasklist /s "his computer name"

And it gave me this message " Type the password for "my computer name"/"my account name":

The only problem is, I don't have a password. I just can't figure this one out. Do I need to make the /s more specific?

You need the password of his machine to join it from across the domain. You may even need Administrator Rights, depending how they have things locked down.

Ah, dang. I guess I could password dump it and then just bruteforce the password, but that would take days and for very little accomplished. Thanks a lot. You can lock this now.