What is this behaviour called?

[nevernotstruggling]

Happens in queues quite a bit when a random stranger starts complaining to you about the queue or whatever when you also have no control over the situation.

The response they want from you is equal outrage and negativity. If it's not reciprocals the whole exchange is really awkward.

Also happens to me with people I know. I/someone we know has organised a lovely activity but it's critiqued as soon as we arrive and the complainer makes everyone feel a bit shit and awkward.

The people in queues are not complaining to you, they are complaining about the situation they have found themselves in, and presumably you are equally inconvenienced too, since you are standing beside them.

As for the people you know, well some folks like to rain on other people's parade. Tell the complainer that they can either STFU or organise it themselves next time.

Oh I hate it when that happens. Not sure what to call it except...'misery loves company'?
'complaints connection'?
'Presumptous'?

I just go hehe yea yea yea hehe yea
While they're speaking.
I add nothing else to it.

If they've only just made one comment, I do same thing just shorter in agreement neutrality.

The complainer feels better after 5 seconds mini rant/comment and turns away, probably knowing it was a bit awkward and I had actually said nothing.

It will be a lot awkward if I chime in with "Well actually I think... " no matter how nicely I do it. I hate awkward situations so this is easier.