I work at a small company and a few months ago this incident occurred: I was excited and wanted to quickly show my colleague something who was standing nearby. As what I wanted to show him was important, I gently touched his elbow and hurried him over (with my hand on his arm) to see what I wanted to show him. We were friends or at least friendly with each other and in my mind this was a totally normal level of physical contact for the situation. I completely forgot about this until about a week later, I was informed that he had filed an official complaint of physical harassment. Long story short, we went through some official mediation and everything worked out "fine". There was also security footage of the incident which we weren't allowed to see. Needless to say, we aren't too cordial anymore but things are overall OK.
Later one of his friends in the office make a subtle joke/snide remark about it at a company wide meeting. I was pretty shocked and said nothing at the time but I'm wondering how I should have handled the situation and how I should going forward.