Menu drop downs that are secretly buttons, too.
Paypal did this to me. Apart from the greater peeve that Paypal won’t let you emigrate (seriously: you have to close your account and open a new one if you change your country), the help says to select Account – Profile – Close Account. Fair enough. But if you select Account, and then mouseover Profile, you get a dropdown menu of four items, none of them Close Account. You have to click on Profile to get the full menu.
I appreciate this is a UI shortcut to the popular options, but there should be some UI hint the Profile is a link, as well as a dropdown heading.