In Joker we can often see Arthur dancing (or doing some sort of approximation of a "clown dance"), but on a few occasions, this dance looks very forced and unnatural: his whole body is tense while his arms make some Tai-chi moves.
We can see it at least twice:
In the bathroom after killing the three guys in the subway and just before he enters the Murray show.
Is it possible that this is some sort of medical condition? OCD movement?