Consequently, the same guide advises not to put it in direct contact with other credit cards or loose items so that you do not scratch the pristine titanium surface. And if there is a stain you can clean, you will wipe it down with a microfiber cloth moistened with isopropyl alcohol.
This is not a functional question about the level of Antennagate. It's not like your card will stop working just because it's a little dirty, and you'll have an incentive to use Apple Pay more often anyway. That said, the titan card is as much about flaunting your status as it is making purchases. It's hard to do that when your card looks like it went through hell, right?