Ticket Taker has 6 main sprites, all of which he has atleast one arm behind his back. You could say that it's simply because it's easier to draw, however, he does this everywhere except for three scenes, (not counting his human disguise in day 1. or the Columbina mirror) two of which are in the mirror tent, his performance. It's something he has full control over, and with him being the weakest in physical strength, it may grant him a feeling of safety aswell.
In the scenes with his arms out, he's seemingly inside of the mirrors. Instance 1 being at the bidding, although just a shadow, it looks that his arms are actually infront of him. Instance 2, the sequence of his various 'forms' walking and 'merging' into the middle, instance 3 is when he is pushing through the blue mirror. Even when he's grabbing your wrist after bumping into Carol, if you hide the textbox, he has an arm behind his back.
There are 4 sprites (if you include the wrist grab, albeit, not one of his main sprites.) that show him with one arm behind and one out, 3 out of 4 he uses his right hand. It's been stated that he's right handed, so that isn't too out of the ordinary.
Rolling back to his human disguise in day 1, while yes, his hands are not behind his back, he does have a booth seat behind him, so that'd be a bit of an awkward way to sit. His left hand is on the table, as for the other, I'd assume it's resting on his thigh. You should also note that this occurs in a public area, which also just so happens to be your work-place. If you were to get violent with a customer, you'd surely get fired or even sued if any severe harm were to be caused.
In day 2, you briefly see the disguise again, his back is left fully vulnerable, one hand by his side, the other in a shushing position. With the lack of frames, it's a bit hard to truly tell, but it's safe to assume that the animation is displaying a brisk walk. I actually think under normal day-to-day circumstances, he'd walk with his arms crossed behind his back. It's possible that Ticket Taker has had experiences that've caused him to be paranoid about protecting his back around humans.
In the Columbina mirror + eating cutscenes, you can't really tell how he's positioned.
External to the game, in his solo birthday art, the chibi has his arms behind his back. (Also his feet angled the same as his fullbody sprites but that's unrelated.) The chibi for Pierrot's birthday art, his arms are infront of him, back to Jester, who is pulling at his coattails. The other occurance of his arms crossing against his chest is during the bidding which I mentioned earlier. From this, it's safe to say he trusts the other monsters to not hurt him.
I'm not going to count the chibi in Harlequin's birthday art since he's just tied up.
In the comic relating to Pierrot's past and the old costumes, he doesn't show this behavior at all. His body language is actually quite loose and free in comparison to him now.
