Here are a couple of things I thought people might be interested in that I gleaned from the "Big Wheel" script.
This is what the script says when Vincent is sticking his tongue out, looking in the mirror:
INT. VINCENT'S APARTMENT/KITCHEN - DAY
Water runs down a white enameled sink, escaping through the metallic sink strainer. Vincent obsessively cleans his hands. Washes his face.
VINCENT
(On the roof of his mouth)
Cluck! Cluck!
Glasses off. He rises up. Dries his face. Looks at the black plastic covered mirror. He pulls down the plastic. Cautiously. Gazes back at his face. Opens his mouth wide. Sticks out his tongue. Why? He's crazy.
So the script doesn't really give much illumination as to why he does it... just 'cause he's crazy.
At the amusement park, near the end of the episode:
Stanley reaches for Vincent's hand. Vincent offers his arm instead, avoiding human contact.
And then, at the very end:
Stan reaches out for Vincent's hand. In the final moment's [sic] of Vincent's life, he takes Stanley's hand in his. The wheel turns slowly round. The world beneath rising to greet them.
STANLEY
I wish you could be my dad.
VINCENT
(whispers)
Forgive me.