I recently (reluctantly) attended the biennial mandatory sexual harassment seminar at my workplace.
The outside agitator - er instructor related an anecdote about a poor chap that went around with his hands at his sides, his eyes on the floor, never even addressing anybody unless he had to, and certainly never touching anybody (male or female).
You guessed it - the subject of a sexual harassment complaint.
It seems you have to "acknowledge" someone's presence and "notice" them. You just can't "acknowledge" or "notice" too much or in a way that "creates a hostile environment" in the mind of the complainant.
Two hours of male bashing, and I still don't know how to avoid a complaint.