(Pro) Disconnecting from other Macs

[grun]

Hello,
My school computer is a MacBook Pro. At the beginning of the year, I would connect to my friends' computers (after figuring out their passwords, which are the same format for everyone here) to prank them by putting things on their desktop. I had a close shave with getting in trouble for this.
I haven't actually gone into their files since, but my computer keeps automatically connecting to their computers. I can't clear my keychain completely because I'm connected to the school server, and I would rather not risk opening the window in which I'm connected to them.
Any suggestions? I've tried hitting Disconnect, but it keeps reconnecting.

 

[Kaveman]

Use Keychain Access, locate their user name, it has search. Then delete it.