From AN 7.68, we find what is meant by one with a sense of social gatherings:
“And how is a monk one with a sense of social gatherings? There is the
case where a monk knows his social gathering: ‘This is a social
gathering of noble warriors; this, a social gathering of brahmans;
this, a social gathering of householders; this, a social gathering of
contemplatives; here one should approach them in this way, stand in
this way, act in this way, sit in this way, speak in this way, stay
silent in this way.’ If he didn’t know his social gathering—’This is a
social gathering of noble warriors; this, a social gathering of
brahmans; this, a social gathering of householders; this, a social
gathering of contemplatives; here one should approach them in this
way, stand in this way, act in this way, sit in this way, speak in
this way, stay silent in this way’—he wouldn’t be said to be one with
a sense of social gatherings. So it’s because he does know his social
gathering—’This is a social gathering of noble warriors; this, a
social gathering of brahmans; this, a social gathering of
householders; this, a social gathering of contemplatives; here one
should approach them in this way, stand in this way, act in this way,
sit in this way, speak in this way, stay silent in this way’—that he
is said to be one with a sense of social gatherings.
In Iti 21, the Buddha explains the benefit of having a confident mind:
“Here, bhikkhus, some person has a confident mind. Having examined his
mind with my mind, I know that if this person were to die at this
time, as if carried there he would be placed in heaven. What is the
reason for that? It is because his mind is confident. It is because of
the mind’s confidence that some beings here, when the body perishes,
are reborn after death in a good bourn, in a heavenly world.”
Here's an excerpt from the essay by Thanissaro Bhikkhu on "Social Anxiety":
It's interesting that Ajaan Lee focuses on what other people say as
one of the tests for a mind that's really at peace. The Buddha makes a
similar point in one of the Dhammapada verses. "If, when other people
say harsh things to you and you don't reverberate — like a cracked
gong — that's a sign that you've attained true peace of mind." This
might seem strange. Why does the test lie in how you react to what
other people say?
The mind is very sensitive to this issue. We learn very early in our
lives that our happiness is going to depend on how other people treat
us. As children, we're surrounded by people a lot more powerful than
we are, so there's always a sense of fear built into our relationships
to the people around us. We become sensitive to other people's moods,
sensitive to what they might do, what they might say. As a result, our
center of gravity is placed outside because we're afraid of them, and
we try to put up a wall outside ourselves to protect ourselves from
them.
What this means is that our psychic center of gravity gets moved
outside the body. If you've ever taken any martial arts classes, you
know that if your center of gravity is outside your body you're in bad
shape. You're in a weak position.
Now the Buddha doesn't say to ignore other people and just be very
selfish. He says there's a different way to approach the whole issue
of happiness. In other words, you find a source for happiness that
doesn't take anything away from anyone else, so you don't have to be
afraid of other people. When you're not afraid of them, you find that
you can actually be more compassionate to them. So developing and
maintaining this center inside is not a selfish thing. The Buddha's
not teaching you to be insensitive. He's just saying to put yourself
in a stronger position and to trust that you're stronger by not trying
to go outside and fix up people's moods and all the other things that
we think we can do with other people when we're dealing with them.
Just stay inside and have a sense of confidence that you're strong
inside. After all, your source of happiness lies inside. Because it's
not taking anything away from anybody else, you don't have to be
afraid of them.
Yuttadhammo Bhikkhu also has a nice YouTube video talk on the Dhammapada verses on the broken gong.