lmao, strong muscle baby.

some points:
stance is pretty awkward, not sure what you were you trying to go for.
AA is pretty bad, what is the background colour it is intended to be used on?
pretty hard to explain in words what's wrong with the anatomy, since it's such a small picture (and body frame), but here's a quick edit, maybe it'll help a bit. You should look for some references if you can't remember where every muscle originates from and inserts, or simply study anatomy in general; it'll help you a bunch.

also, y no leg muscles?

haha
it's meant to be a silly sprite, not really perfect anatomy/ perfect muscles.. and not supposed to be hulk, but a skinny defined guy.
on the pose he is supposed to be flying, flexing muscles like left one (our view) would be forearm going up, and the right one (our view) would be forearm going down (also flexing though)
here's a sketch incase I didn't explain that well
I had the other arm going downwards so the abs would show.. on your edit the abs are hidden

some small edit, still don't know what to do with his left arm.. .. (and this is the background color)

Edit: as for legs.. since I planned out the sprite I wanted them to have feet facing each other, it's kind of 'stylistic' touch
thanks for your critique :- )

Nice work 

I made a edit on the curtains to make them blend in more, and made the windows same size

I understand the triangle form, but the thing is that the front is narrowing on one side in a different angle than on the other, while they start with same width, at the end the left side is at least 80% thinner than the right, so the very end of the car is looking almost side-view since you even removed the metal part showing on the left side.

There were some things bugging me about the car, I made a edit since I don't think I'd be good at explaining it..