From a more practical position, here are some reflections. I am sure others have their won approaches.
First of all, place importance on one's own practice. Kindness can be applied in situations that call for firmness or other actions perceived as unpleasant. Being kind to the person or people one is leading is always possible (even though we all fail at times), and important to distinguish from approval. We can accept the person without approving of their actions.
Another suggestion is to avoid speaking and acting out of anger (or any type of aggression). This is where the practice becomes so important, because the more, the deeper, we practise, the more we are able to accommodate.
To quote the Dalai Lama
Do not let the behavior of others destroy your inner peace.
As they say, ´Being a pacifist does not mean being a passive-ist´ - there is nothing stopping correction of behavior (coming late, abusing others, and the rest of the long list), but the opportunity is always there to do it with kindness towards the person. Even if you have to fire somebody for not doing their job properly, you can have compassion for them and try to be helpful.
Should you be presented with anger from the person or people you lead, trying to see their view also helps, especially in discovering the underlying cause of the anger (the attachments, and so on).
On the practice part, specifically on handling ill-will (anger and other), here is a note from the Pali Canon (Access To Insight):
Six things are helpful in conquering ill-will:
- Learning how to meditate on loving-kindness;
- Devoting oneself to the
meditation of loving-kindness;
- Considering that one is the owner and
heir of one's actions (kamma);
Frequent reflection on it (in the
following way): Thus one should consider: "Being angry with another
person, what can you do to him? Can you destroy his virtue and his
other good qualities? Have you not come to your present state by your
own actions, and will also go hence according to your own actions?
Anger towards another is just as if someone wishing to hit another
person takes hold of glowing coals, or a heated iron-rod, or of
excrement. And, in the same way, if the other person is angry with
you, what can he do to you? Can he destroy your virtue and your other
good qualities? He too has come to his present state by his own
actions and will go hence according to his own actions. Like an
unaccepted gift or like a handful of dirt thrown against the wind, his
anger will fall back on his own head."
— Commentary to Satipatthana Sutta
These things, too, are helpful in conquering ill-will:
- Rapture, of the factors of absorption (jhananga);
- Faith, of the spiritual faculties (indriya);
- Rapture and equanimity, of the factors
of enlightenment (bojjhanga).
As a summary, I would like to reiterate that we can always have kindness for the person, for the situation, and for our own reactions (they are based on conditions, after all) - allowing for increasing acceptance with more practice.