I'm lucky my dad uses a different password for his gmail account than his linkedin login (using said gmail address). He was stuck for a while complaining that he couldn't log in. Turned out he was already logged in, and LinkedIn was just presenting him with a "put your gmail password in here so we can raid your contacts" box. It looks just like the login page, so he kept putting in his LinkedIn (not gmail) password and it kept saying "your password is incorrect."

What a shitty thing to do.