First off to be "mentally healthy" does not exclude the absence of negative experiences, emotions, or responses. An ability to successfully cope with every single good, bad, even neutral thing that comes our way is not required for mental health.
To be generally "emotionally well adaptive" and able to successfully interact with peers most of the time would signify a high degree of mental health. But, there may be situations that cause distress that affects the same person's behavior.
A person is grieving because they have lost a loved one may, for example cry a lot. Indeed, a woman going through menopause do so as well. It is very often not fun to be around people who are going through a divorce or break up. People who are perpetually angry over financial problems are viewed as justified. Sometimes people having a bad day get an armchair diagnosis from coworkers who do not like them.
The point is there are times when we fail to adapt to environments and events well and are not the perfect picture of mental health. The day or some days later or time later we see\are back to the picture of contrast between ourselves and our grumpy neighbor.
Those maladaptive behaviors do not rise to the level of mental illness. We all know, or and are these people. There are people who do not meet the criteria of mental illnesses but do react to their environments some events with responses that are extreme. They are sometimes people we have known and "broken up with" for one reason or in one way or another.
The behavior of someone who is considered mentally healthy, but angrily trashes house that the bank foreclosed on is not necessarily mentally ill, but most definitely is adapting to those circumstances in an extremely very maladaptive way.
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