I work in an office of cubicles and there is this one guy (who I have worked with for 5 years) who will approach my cubicle, not say a word and not need anything from me. Rather, he is there to return a folder or ask another coworker a question but he always approaches me first or he might be taking to another coworker but looking at me. Sometimes he ignores me for days and other times he approaches my desk for no reason other than to let me know he's there. He doesn't even speak to me, just looks at me and walks away. What is wrong with this guys? Any advice?