Mordecai is normaly very uncomfortable with any sort of intimacy/contact
Which is pretty understandable considering his naturally introverted nature, combined with his rough backround working as a young book keeper for the mob in New York, and lack of social connections with people outside of his family, it would be very hard for him to relax/feel safe enough around someone to allow casual touch
But if there is anyone in St Louis that he trusts enough to let his guard down enough to allow at least a little casual contact it would be Viktor
During their Defiance chess match he voluntarily got so much into Viktor's personal space, he almost pushed the cap off his head
Got pretty close to and was looking down at his muzzle as well
He just reaches a point, not too long after starting to work with him, where he stops seeing Viktor as a potential threat like most other people, and instead as a safe reassuring prescence that he can relax a little bit around
Someone he even feels safe and comfortable enough to tease a little about his fashion, grooming etc
Viktor "Vinegar" Vasko is a giant tank of a man that can feeeze people with fear with a one eyed death glare and rip their limbs off with his bare hands, and yet Mordecai is certain he is in no danger when he does this
Mordecai is usually either indifferent or uncomfortable with others opinions and judgement of him or his behaviour
But Mordecai wants Viktor to have a good opinion of him, or at the very least not think badly of him.
Whether its his appearance, professional abilities, or how well he responds or handles situations generally
In his own repressed, stunted way, he seems to want to be as close to Viktor as he can get without either stepping entirely out of his own comfort zone, or in turn doing something that could make Viktor uncomfortable to be around him
To be as close to intimate without stepping over an unspoken rule/invisible line
How better to do that than to involve Viktor in his passions for dapper fashion and symmetry by making their style match?
First with a very small relatively casual thing like getting Viktor into an identical red tie for Christmas
Then escalating to matching suits by New Years 1926, made in Viktor favourite colour of slate blue (which Mordecai had taken note is the colour he wears the most often even if Vikor himself hasn't really though about it) and with double breasted waistcoats that Viktor seems to prefer
Then as the cherry on top got them into symmetrical positions for the group photo
While Viktor may have rolled up the sleaves and taken the tie off, Viktor was clearly now used to Mordecai's quirks and willing to indulge it
How self aware Mordecai is about the reasons for this painfully indirect and roundabout expression of his need for Viktor is debatable
But he may know in some way that he can't have what he really wants deep down
Having broken the bond he had built with Viktor entirely, in a misguided effort to remove him from the danger of the dying Lackadaisy while he risks his skin spying on Marigold, all Mordecai has achieved has been to give himself another wound next to the one Atlas's death left
One so big he will bare his soul to a random thug named Gracie Grombach, just because he looks like a Dollar store Viktor Vasko