Chris, a manager at work, stopped by my cubette to review his PowerPoint slide with me. I brought it up, full screen, on my monitor, and we talked at length. He leaned in and proceeded to emphasize each of his points by drawing his slightly damp fingertips in circles and lines back and forth across the glass. His whole palm pressed onto the surface at one point, to clearly indicate what part of the screen I should ignore due to its status as work-in-progress.
In truth, I didn't mind the smearing. In fact, I was surprised by how in-check this particular neurosis of mine seemed to be. His enthusiasm for this project - and his willingness to really listen to collaborator input - is infectious, and a sign of his maturity as a manager.
A good amount of credit was deposited into his account at the Bank of Good Favor I keep for coworkers.