My worst Skype annoyance was when they seized your purchased credits if your account was left unused for 180 days. As a sporadic user of Skype when I needed to place an international call etc, having purchased credits reset automatically was such a provocation [0]. Every time I have to re-install Skype for some reason, there's always a new regression or dark UX pattern in use.
[0] https://blogs.wsj.com/digits/2010/01/14/skype-lawsuit-to-yie...