Other liquids
Everyone's having a laugh about the drink spills, but cockpit equipment SHOULD be water-resistant. It's life-or-death equipment and a pilot's drink isn't the only possible source of intrusion. There have been a few passenger jets that had their windscreens destroyed/removed in flight for various reason. If it happened to be raining at the time, you'd have quite a bit more than a coffee-cup worth coming in. The cost of improvements is much less than the cost of one accident.
Biting the hand that feeds IT
