Coffee
A long time ago Collins had a problem with a control head having a high failure rate. It was determined that the control heads were filling up with beverages and corroding the switch contacts. A service bulletin was issued instructing where to drill holes to let the coffee drain out...
We post coat boards now a days, and don't use open frame switches as much. You might get unlucky and make a control head inop, but it is more likely you will just make the push buttons sticky (if you like sugar in your coffee).
Not recommending coffee baths for the avionics, but I highly doubt you could cause much more than an annoyance by doing so.