Or, similarly, I set up an HTTPS proxy on my Mac, and set Wireshark to listen. Then, had someone else log in to a different account (say, the guest account) on the machine, and asked them to log into gmail, say, as usually via HTTPS (with a fake user/pass). A warning does pop up about "insecure connection", but most people just dismiss it and go ahead and log in - and wireshark intercepts username and password.
Classic MiTM, well known, but still freaky to observe how easy it is to set up.
Classic MiTM, well known, but still freaky to observe how easy it is to set up.