Dice have had giant buckets of ritual, ceremony, and superstition since before there were dice. I have no doubt that cave-men were blowing on their knucklebones before tossing them into a circle of goat entrails and that roman soldiers were rubbing their dice on whoever was winning to pick up some of their luck.
Gamers are no different and despite the fact that many gamers are rational people who understand things like probability and the most basic physics of tossing a geometric shape onto a hard surface, we have created a whole lot of our own.
Here are a few I have personally witnessed:
Priming new dice by rolling them with the old ones… Sort of an initiation to your collection.
Never mixing new dice with old… I’m not sure when new dice become sufficiently old to join the general population.
Only use dice for their particular game… Never use your D&D dice when playing GURPS.
Never letting these sets of dice see each-other in case they got jealous.
Placing dice with the most desired result face up and keeping them that way until the roll.
Placing dice with the worst possible result face up and keeping them that way until the roll.
Rolling dice for ‘practice’ before playing.
Not rolling dice when not needed so you don’t use up the good rolls.
Rolling the dice a whole lot pre-game to use up the bad rolls.
Switching to new dice when one is rolling poorly.
Removing dice from your collection when they roll bad so they don’t infect the rest.
Not letting anyone touch your dice.
Making someone else use dice that are rolling poorly so they change their luck.
Buying a new set for each new campaign.
Keeping sets of dice for different purposes within the game… one set to roll stats, one set to make attack rolls, maybe even a specific die for a specific skill roll.
Rolling different dice of the same type to select the ones that roll best for that nights session.
Destroying poorly performing dice in front of the rest as an example… I knew one person who had a special sledgehammer specifically for this purpose.
Pleading with your dice while shaking them.
Threatening your dice while shaking them.
Kissing or blowing on the dice before each roll.
Having a pretty girl/boy kiss them.
I even knew one person who convinced a priest to bless his dice, no mean feat in the 80s when a lot of people thought that D&D equated murdering your friends while worshiping Satan in storm drains.
I had one superstition I tried to get started at one point, but it never got much traction… Touching your dice to a published game designer, the bigger a game line the better your dice would do. This may or may not have resulted in one or two people tagging Gary Gygax at conventions. I had managed Mike Pondsmith myself.
In short; People are crazy, gamers are people, therefore gamers are crazy.