This problem multiplies even more as Hart and Blackmon report: “Clinical experience shows that underassertive and excessively overassertive ministers are much more likely to suffer from depression, burnout, helplessness and especially problems with anger and resentment."
Source: wiktionary
I once heard someone offer an underassertive friend a favor and the friend said no in such a roundabout fashion that the person actually thought she'd said yes, and did it anyway.
Source: wiktionary
Some people are underassertive in almost every kind of social situation, whereas others behave overassertively in social encounters.
Source: wiktionary