Superstitions in the hangar:

It's bad luck to get the unit insignia on your 'mech shot off. It's extremely bad luck if, if it's a face or head of some kind, it gets a shot through the eye.
Burn, or at least thoroughly wash and swap for another, any pilot gear you were wearing in a 'mech that got destroyed. Metal-death sticks deep.
In certain units, you have to address your 'mech by its full serial code until you've had your blood spilled on it. (Shrapnel, glancing shots, purposeful sacrificial incisions, however you do it.) Only then do you give it a name.
Any 'mech that uses fire as its primary weapon has to face inwards in its niche or bay. (There's a reason for this one. Backing out is tricky, and any obstacle that can be put in the path of burning people to death, people generally try to ensure is.)
Never gamble in the hangar. Not even flipping a coin. You don't want them learning to leave things to chance.
No sleeping in your cockpit. A 'mech's interior, in superstition, should not be your comfy spot- otherwise you get too relaxed, and don't stay as wary as you should.
If a 'mech got a pilot shot out of or through the cockpit, keep said cockpit open whenever it's not in action for at least a week. Make sure they've had time to pack their things out. Then keep it shut for a full night, in some traditions with a last packet of energy gel or similar outside it.