One thing that annoys me about Teamviewer: as soon as you open the window on the desktop application (in both Windows and Ubuntu) to the 'Remote Control' tab, your ID and Password for remote control are prominently displayed.
(Image stolen from this question.)
There's something inherently bothering about being able to configure 10-digit, randomly generated password, that can be seen easily (and without much effort at all) by someone who just happens to walk past my workstation.
It seems likely that the problem can be circumvented by using the whitelist feature, but that seems like overkill here, considering the problem could be solved by the digital equivalent of a sticky note covering the screen.
Considering this is such a glaringly annoying feature, I'm surprised not to have found anybody else complaining about this...