Two useful shortcuts for managing known wifi networks on OS X.
If you've got a modern Mac with no Ethernet, your wifi interface is en0. Otherwise, it is en1, so replace that below.
alias wifils='networksetup -listpreferredwirelessnetworks en0'This lets you list (and possibly grep) all known, previously connected wireless networks. Just type wifils.
alias wifirm='networksetup -removepreferredwirelessnetwork en0 'This lets you remove networks from the known list, preventing connection in the future. Just type wifirm <network name>.