It's a late and Lucifer can't sleep. He heads downstairs for a nightcap and finds more than he expects.
AKA
Alastor likes to cook in the middle of the night and these two can't go two minutes without throwing hands.
when Alastor was human has was constantly used and bullied for his skin and hair. Now in hell he hides a lot of his characteristics for example his HATE for touch and forces himself to deal with it.
or
Alastor is to tired to deal with acting 'normal' and just does what feels comfortable.
or
Alastor angst, its good give it a lick before throwing it away.