what's the meaning of "squirming around" and "I'm about done fussing with you" meaning of 'fussing''
that's from movie "secret window "
and here's the text :
Jesus, Mort.

W-Where'd you get
that old thing? The attic?

(WITH A SOUTHERN ACCENT)
It's mine.

Wasn't ever anybody else's.

Mort, what's wrong?

You got you
a wrong number, missus.

(GASPS)

Ain't no Mort here.

Mort's dead.

He did a whole lot
of squirming around

but in the end he couldn't lie
to himself anymore,

let alone to me.

Now, I never put a hand on him,
missus. I swear.

He took the coward's way out.

Why are you talking
this way, Mort?

That's just the way I talk.

You're scaring me.

It don't matter.

You won't be scared long.

(GASPS)

(YELLS)

(♪)

Oh, God. Oh, God.

(ENGINE STARTS)

(ENGINE REVVING)

(SCREAMS)

(SCREAMING)

I'm about done fussing with you.

Question

what's the meaning of "squirming around" and "I'm about done fussing with you" meaning of 'fussing''
that's from movie "secret window "
and here's the text :
Jesus, Mort.

W-Where'd you get
that old thing? The attic?

(WITH A SOUTHERN ACCENT)
It's mine.

Wasn't ever anybody else's.

Mort, what's wrong?

You got you
a wrong number, missus.

(GASPS)

Ain't no Mort here.

Mort's dead.

He did a whole lot
of squirming around

but in the end he couldn't lie
to himself anymore,

let alone to me.

Now, I never put a hand on him,
missus. I swear.

He took the coward's way out.

Why are you talking
this way, Mort?

That's just the way I talk.

You're scaring me.

It don't matter.

You won't be scared long.

(GASPS)

(YELLS)

(♪)

Oh, God. Oh, God.

(ENGINE STARTS)

(ENGINE REVVING)

(SCREAMS)

(SCREAMING)

I'm about done fussing with you.

Answer

Squirming means fidgeting, wriggling, not holding still--in this case metaphorically. Children squirm (literally) when they don't want to be held or can't sit still. The person in question tried to squirm away from the truth. "I'm about done fussing with you," has a coloquial flavor. "About" means "almost", but could really mean "more than" in this context. "Fussing" here means dealing with, bothering with, putting up with, being inconvenienced by, having to attend to. The person speaking is saying I'm tired of dealing with you (or your behavior) and don't expect me to continue.

Answer

"I am about done fussing with you"

"I am done with" = I am finished with you
"About" an additional word, without any extra meaning
"Done fussing" = fussing means bothering with, troubling oneself with
I am done fussing/toying with you (with or without 'about") = I am finished bothering/troubling myself with you.

Basically, it means "I am done!", "this is enough!", "never again!".

Answer

These terms are being used along with the accent to suggest a somewhat non-standrad way of speakiing.

"squirming around" 
Means moving, as if not sitting still on your chair. As if to get comfortable,. you must keep moving to try to find a comfortable position.
Here it is used to suggest that Mort may have tried many things to get comfortable, with, life, maybe, what was going on, but could not get comfortable, could not accept things.

and "I'm about done fussing with you"

Fussing is to pay attention, excessive attention.
Generally means to be particular. 
Stop fussing with those flowers!
But, I want them to look just right. Nothing less than perfect will do.
.
Here fussing with - means the same, paying attention. Doing  things related to ...

Answer

"Squirming around" = stupidly & hopelessly moving around, trying to escape danger